/**
*******************************************************************************
* Copyright (C) 1996-2006, International Business Machines Corporation and    *
* others. All Rights Reserved.                                                *
*******************************************************************************
*/

package com.ibm.icu.text;

import com.ibm.icu.impl.UCharacterProperty;
import com.ibm.icu.impl.NormalizerImpl;

/**
 * <p>Standalone utility class providing UTF16 character conversions and
 * indexing conversions.</p>
 * <p>Code that uses strings alone rarely need modification.
 * By design, UTF-16 does not allow overlap, so searching for strings is a safe
 * operation. Similarly, concatenation is always safe. Substringing is safe if
 * the start and end are both on UTF-32 boundaries. In normal code, the values
 * for start and end are on those boundaries, since they arose from operations
 * like searching. If not, the nearest UTF-32 boundaries can be determined
 * using <code>bounds()</code>.</p>
 * <strong>Examples:</strong>
 * <p>The following examples illustrate use of some of these methods.
 * <pre>
 * // iteration forwards: Original
 * for (int i = 0; i &lt; s.length(); ++i) {
 *     char ch = s.charAt(i);
 *     doSomethingWith(ch);
 * }
 *
 * // iteration forwards: Changes for UTF-32
 * int ch;
 * for (int i = 0; i &lt; s.length(); i+=UTF16.getCharCount(ch)) {
 *     ch = UTF16.charAt(s,i);
 *     doSomethingWith(ch);
 * }
 *
 * // iteration backwards: Original
 * for (int i = s.length() -1; i >= 0; --i) {
 *     char ch = s.charAt(i);
 *     doSomethingWith(ch);
 * }
 *
 * // iteration backwards: Changes for UTF-32
 * int ch;
 * for (int i = s.length() -1; i > 0; i-=UTF16.getCharCount(ch)) {
 *     ch = UTF16.charAt(s,i);
 *     doSomethingWith(ch);
 * }
 * </pre>
 * <strong>Notes:</strong>
 * <ul>
 *   <li>
 *   <strong>Naming:</strong> For clarity, High and Low surrogates are called
 *   <code>Lead</code> and <code>Trail</code> in the API, which gives a better
 *   sense of their ordering in a string. <code>offset16</code> and
 *   <code>offset32</code> are used to distinguish offsets to UTF-16
 *   boundaries vs offsets to UTF-32 boundaries. <code>int char32</code> is
 *   used to contain UTF-32 characters, as opposed to <code>char16</code>,
 *   which is a UTF-16 code unit.
 *   </li>
 *   <li>
 *   <strong>Roundtripping Offsets:</strong> You can always roundtrip from a
 *   UTF-32 offset to a UTF-16 offset and back. Because of the difference in
 *   structure, you can roundtrip from a UTF-16 offset to a UTF-32 offset and
 *   back if and only if <code>bounds(string, offset16) != TRAIL</code>.
 *   </li>
 *   <li>
 *    <strong>Exceptions:</strong> The error checking will throw an exception
 *   if indices are out of bounds. Other than than that, all methods will
 *   behave reasonably, even if unmatched surrogates or out-of-bounds UTF-32
 *   values are present. <code>UCharacter.isLegal()</code> can be used to check
 *   for validity if desired.
 *   </li>
 *   <li>
 *   <strong>Unmatched Surrogates:</strong> If the string contains unmatched
 *   surrogates, then these are counted as one UTF-32 value. This matches
 *   their iteration behavior, which is vital. It also matches common display
 *   practice as missing glyphs (see the Unicode Standard Section 5.4, 5.5).
 *   </li>
 *   <li>
 *     <strong>Optimization:</strong> The method implementations may need
 *     optimization if the compiler doesn't fold static final methods. Since
 *     surrogate pairs will form an exceeding small percentage of all the text
 *     in the world, the singleton case should always be optimized for.
 *   </li>
 * </ul>
 * @author Mark Davis, with help from Markus Scherer
 * @stable ICU 2.1
 */

public final class UTF16
{
    // public variables ---------------------------------------------------

    /**
     * Value returned in <code><a href="#bounds(java.lang.String, int)">
     * bounds()</a></code>.
     * These values are chosen specifically so that it actually represents
     * the position of the character
     * [offset16 - (value >> 2), offset16 + (value & 3)]
     * @stable ICU 2.1
     */
    public static final int SINGLE_CHAR_BOUNDARY = 1,
        LEAD_SURROGATE_BOUNDARY = 2,
        TRAIL_SURROGATE_BOUNDARY = 5;
    /**
     * The lowest Unicode code point value.
     * @stable ICU 2.1
     */
    public static final int CODEPOINT_MIN_VALUE = 0;
    /**
     * The highest Unicode code point value (scalar value) according to the
     * Unicode Standard.
     * @stable ICU 2.1
     */
    public static final int CODEPOINT_MAX_VALUE = 0x10ffff;
    /**
     * The minimum value for Supplementary code points
     * @stable ICU 2.1
     */
    public static final int SUPPLEMENTARY_MIN_VALUE  = 0x10000;
    /**
     * Lead surrogate minimum value
     * @stable ICU 2.1
     */
    public static final int LEAD_SURROGATE_MIN_VALUE = 0xD800;
    /**
     * Trail surrogate minimum value
     * @stable ICU 2.1
     */
    public static final int TRAIL_SURROGATE_MIN_VALUE = 0xDC00;
    /**
     * Lead surrogate maximum value
     * @stable ICU 2.1
     */
    public static final int LEAD_SURROGATE_MAX_VALUE = 0xDBFF;
    /**
     * Trail surrogate maximum value
     * @stable ICU 2.1
     */
    public static final int TRAIL_SURROGATE_MAX_VALUE = 0xDFFF;
    /**
     * Surrogate minimum value
     * @stable ICU 2.1
     */
    public static final int SURROGATE_MIN_VALUE = LEAD_SURROGATE_MIN_VALUE;
    /**
     * Maximum surrogate value
     * @stable ICU 2.1
     */
    public static final int SURROGATE_MAX_VALUE = TRAIL_SURROGATE_MAX_VALUE;

    // constructor --------------------------------------------------------

    ///CLOVER:OFF
    /**
     * Prevent instance from being created.
     */
    private UTF16()
    {
    }
    ///CLOVER:ON
    // public method ------------------------------------------------------

    /**
     * Extract a single UTF-32 value from a string.
     * Used when iterating forwards or backwards (with
     * <code>UTF16.getCharCount()</code>, as well as random access. If a
     * validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">
     * UCharacter.isLegal()</a></code> on the return value.
     * If the char retrieved is part of a surrogate pair, its supplementary
     * character will be returned. If a complete supplementary character is
     * not found the incomplete character will be returned
     * @param source array of UTF-16 chars
     * @param offset16 UTF-16 offset to the start of the character.
     * @return UTF-32 value for the UTF-32 value that contains the char at
     *         offset16. The boundaries of that codepoint are the same as in
     *         <code>bounds32()</code>.
     * @exception IndexOutOfBoundsException thrown if offset16 is out of
     *            bounds.
     * @stable ICU 2.1
     */
    public static int charAt(String source, int offset16)
    {
        char single = source.charAt(offset16);
        if (single < LEAD_SURROGATE_MIN_VALUE) {
            return single;
        }
        return _charAt(source, offset16, single);
    }

    private static int _charAt(String source, int offset16, char single)
    {
        if (single > TRAIL_SURROGATE_MAX_VALUE) {
            return single;
        }

        // Convert the UTF-16 surrogate pair if necessary.
        // For simplicity in usage, and because the frequency of pairs is
        // low, look both directions.

        if (single <= LEAD_SURROGATE_MAX_VALUE) {
            ++ offset16;
            if (source.length() != offset16) {
                char trail = source.charAt(offset16);
                if (trail >= TRAIL_SURROGATE_MIN_VALUE &&
                    trail <= TRAIL_SURROGATE_MAX_VALUE) {
                    return UCharacterProperty.getRawSupplementary(single,
                                                                  trail);
                }
            }
        }
        else
            {
                -- offset16;
                if (offset16 >= 0) {
                    // single is a trail surrogate so
                    char lead = source.charAt(offset16);
                    if (lead >= LEAD_SURROGATE_MIN_VALUE &&
                        lead <= LEAD_SURROGATE_MAX_VALUE) {
                        return UCharacterProperty.getRawSupplementary(lead,
                                                                      single);
                    }
                }
            }
        return single; // return unmatched surrogate
    }

    /**
     * Extract a single UTF-32 value from a string.
     * Used when iterating forwards or backwards (with
     * <code>UTF16.getCharCount()</code>, as well as random access. If a
     * validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">UCharacter.isLegal()
     * </a></code> on the return value.
     * If the char retrieved is part of a surrogate pair, its supplementary
     * character will be returned. If a complete supplementary character is
     * not found the incomplete character will be returned
     * @param source UTF-16 chars string buffer
     * @param offset16 UTF-16 offset to the start of the character.
     * @return UTF-32 value for the UTF-32 value that contains the char at
     *         offset16. The boundaries of that codepoint are the same as in
     *         <code>bounds32()</code>.
     * @exception IndexOutOfBoundsException thrown if offset16 is out of
     *            bounds.
     * @stable ICU 2.1
     */
    public static int charAt(StringBuffer source, int offset16)
    {
        if (offset16 < 0 || offset16 >= source.length()) {
            throw new StringIndexOutOfBoundsException(offset16);
        }

        char single = source.charAt(offset16);
        if (!isSurrogate(single)) {
            return single;
        }

        // Convert the UTF-16 surrogate pair if necessary.
        // For simplicity in usage, and because the frequency of pairs is
        // low, look both directions.

        if (single <= LEAD_SURROGATE_MAX_VALUE)
            {
                ++ offset16;
                if (source.length() != offset16)
                    {
                        char trail = source.charAt(offset16);
                        if (isTrailSurrogate(trail))
                            return UCharacterProperty.getRawSupplementary(single, trail);
                    }
            }
        else
            {
                -- offset16;
                if (offset16 >= 0)
                    {
                        // single is a trail surrogate so
                        char lead = source.charAt(offset16);
                        if (isLeadSurrogate(lead)) {
                            return UCharacterProperty.getRawSupplementary(lead, single);
                        }
                    }
            }
        return single; // return unmatched surrogate
    }

    /**
     * Extract a single UTF-32 value from a substring.
     * Used when iterating forwards or backwards (with
     * <code>UTF16.getCharCount()</code>, as well as random access. If a
     * validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">UCharacter.isLegal()
     * </a></code> on the return value.
     * If the char retrieved is part of a surrogate pair, its supplementary
     * character will be returned. If a complete supplementary character is
     * not found the incomplete character will be returned
     * @param source array of UTF-16 chars
     * @param start offset to substring in the source array for analyzing
     * @param limit offset to substring in the source array for analyzing
     * @param offset16 UTF-16 offset relative to start
     * @return UTF-32 value for the UTF-32 value that contains the char at
     *         offset16. The boundaries of that codepoint are the same as in
     *         <code>bounds32()</code>.
     * @exception IndexOutOfBoundsException thrown if offset16 is not within
     *            the range of start and limit.
     * @stable ICU 2.1
     */
    public static int charAt(char source[], int start, int limit,
                             int offset16)
    {
        offset16 += start;
        if (offset16 < start || offset16 >= limit) {
            throw new ArrayIndexOutOfBoundsException(offset16);
        }

        char single = source[offset16];
        if (!isSurrogate(single)) {
            return single;
        }

        // Convert the UTF-16 surrogate pair if necessary.
        // For simplicity in usage, and because the frequency of pairs is
        // low, look both directions.
        if (single <= LEAD_SURROGATE_MAX_VALUE) {
            offset16 ++;
            if (offset16 >= limit) {
                return single;
            }
            char trail = source[offset16];
            if (isTrailSurrogate(trail)) {
                return UCharacterProperty.getRawSupplementary(single, trail);
            }
        }
        else { // isTrailSurrogate(single), so
            if (offset16 == start) {
                return single;
            }
            offset16 --;
            char lead = source[offset16];
            if (isLeadSurrogate(lead))
                return UCharacterProperty.getRawSupplementary(lead, single);
        }
        return single; // return unmatched surrogate
    }

    /**
     * Extract a single UTF-32 value from a string.
     * Used when iterating forwards or backwards (with
     * <code>UTF16.getCharCount()</code>, as well as random access. If a
     * validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">UCharacter.isLegal()
     * </a></code> on the return value.
     * If the char retrieved is part of a surrogate pair, its supplementary
     * character will be returned. If a complete supplementary character is
     * not found the incomplete character will be returned
     * @param source UTF-16 chars string buffer
     * @param offset16 UTF-16 offset to the start of the character.
     * @return UTF-32 value for the UTF-32 value that contains the char at
     *         offset16. The boundaries of that codepoint are the same as in
     *         <code>bounds32()</code>.
     * @exception IndexOutOfBoundsException thrown if offset16 is out of
     *            bounds.
     * @stable ICU 2.1
     */
    public static int charAt(Replaceable source, int offset16)
    {
        if (offset16 < 0 || offset16 >= source.length()) {
            throw new StringIndexOutOfBoundsException(offset16);
        }

        char single = source.charAt(offset16);
        if (!isSurrogate(single)) {
            return single;
        }

        // Convert the UTF-16 surrogate pair if necessary.
        // For simplicity in usage, and because the frequency of pairs is
        // low, look both directions.

        if (single <= LEAD_SURROGATE_MAX_VALUE)
            {
                ++ offset16;
                if (source.length() != offset16)
                    {
                        char trail = source.charAt(offset16);
                        if (isTrailSurrogate(trail))
                            return UCharacterProperty.getRawSupplementary(single, trail);
                    }
            }
        else
            {
                -- offset16;
                if (offset16 >= 0)
                    {
                        // single is a trail surrogate so
                        char lead = source.charAt(offset16);
                        if (isLeadSurrogate(lead)) {
                            return UCharacterProperty.getRawSupplementary(lead, single);
                        }
                    }
            }
        return single; // return unmatched surrogate
    }

    /**
     * Determines how many chars this char32 requires.
     * If a validity check is required, use <code>
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on
     * char32 before calling.
     * @param char32 the input codepoint.
     * @return 2 if is in supplementary space, otherwise 1.
     * @stable ICU 2.1
     */
    public static int getCharCount(int char32)
    {
        if (char32 < SUPPLEMENTARY_MIN_VALUE) {
            return 1;
        }
        return 2;
    }

    /**
     * Returns the type of the boundaries around the char at offset16.
     * Used for random access.
     * @param source text to analyse
     * @param offset16 UTF-16 offset
     * @return <ul>
     *           <li> SINGLE_CHAR_BOUNDARY : a single char; the bounds are
     *                                       [offset16, offset16+1]
     *           <li> LEAD_SURROGATE_BOUNDARY : a surrogate pair starting at
     *                                          offset16;
     *                                          the bounds are
     *                                          [offset16, offset16 + 2]
     *           <li> TRAIL_SURROGATE_BOUNDARY : a surrogate pair starting at
     *                                           offset16 - 1; the bounds are
     *                                           [offset16 - 1, offset16 + 1]
     *         </ul>
     *         For bit-twiddlers, the return values for these are chosen so
     *         that the boundaries can be gotten by:
     *         [offset16 - (value >> 2), offset16 + (value & 3)].
     * @exception IndexOutOfBoundsException if offset16 is out of bounds.
     * @stable ICU 2.1
     */
    public static int bounds(String source, int offset16)
    {
        char ch = source.charAt(offset16);
        if (isSurrogate(ch)) {
            if (isLeadSurrogate(ch))
                {
                    if (++ offset16 < source.length() &&
                        isTrailSurrogate(source.charAt(offset16))) {
                        return LEAD_SURROGATE_BOUNDARY;
                    }
                }
            else {
                // isTrailSurrogate(ch), so
                -- offset16;
                if (offset16 >= 0 && isLeadSurrogate(source.charAt(offset16))) {
                    return TRAIL_SURROGATE_BOUNDARY;
                }
            }
        }
        return SINGLE_CHAR_BOUNDARY;
    }

    /**
     * Returns the type of the boundaries around the char at offset16. Used
     * for random access.
     * @param source string buffer to analyse
     * @param offset16 UTF16 offset
     * @return
     *     <ul>
     *     <li> SINGLE_CHAR_BOUNDARY : a single char; the bounds are
     *                                               [offset16, offset16 + 1]
     *     <li> LEAD_SURROGATE_BOUNDARY : a surrogate pair starting at
     *                                    offset16; the bounds are
     *                                    [offset16, offset16 + 2]
     *     <li> TRAIL_SURROGATE_BOUNDARY : a surrogate pair starting at
     *                                     offset16 - 1; the bounds are
     *                                     [offset16 - 1, offset16 + 1]
     *     </ul>
     * For bit-twiddlers, the return values for these are chosen so that the
     * boundaries can be gotten by:
     *                    [offset16 - (value >> 2), offset16 + (value & 3)].
     * @exception IndexOutOfBoundsException if offset16 is out of bounds.
     * @stable ICU 2.1
     */
    public static int bounds(StringBuffer source, int offset16)
    {
        char ch = source.charAt(offset16);
        if (isSurrogate(ch)) {
            if (isLeadSurrogate(ch))
                {
                    if (++ offset16 < source.length() &&
                        isTrailSurrogate(source.charAt(offset16))) {
                        return LEAD_SURROGATE_BOUNDARY;
                    }
                }
            else {
                // isTrailSurrogate(ch), so
                -- offset16;
                if (offset16 >= 0 &&
                    isLeadSurrogate(source.charAt(offset16))) {
                    return TRAIL_SURROGATE_BOUNDARY;
                }
            }
        }
        return SINGLE_CHAR_BOUNDARY;
    }

    /**
     * Returns the type of the boundaries around the char at offset16. Used
     * for random access. Note that the boundaries are determined with respect
     * to the subarray, hence the char array {0xD800, 0xDC00} has the result
     * SINGLE_CHAR_BOUNDARY for start = offset16 = 0 and limit = 1.
     * @param source char array to analyse
     * @param start offset to substring in the source array for analyzing
     * @param limit offset to substring in the source array for analyzing
     * @param offset16 UTF16 offset relative to start
     * @return
     *     <ul>
     *         <li> SINGLE_CHAR_BOUNDARY : a single char; the bounds are
     *         <li> LEAD_SURROGATE_BOUNDARY : a surrogate pair starting at
     *                       offset16; the bounds are [offset16, offset16 + 2]
     *         <li> TRAIL_SURROGATE_BOUNDARY : a surrogate pair starting at
     *               offset16 - 1; the bounds are [offset16 - 1, offset16 + 1]
     *     </ul>
     * For bit-twiddlers, the boundary values for these are chosen so that the
     * boundaries can be gotten by: [offset16 - (boundvalue >> 2), offset16
     *                                                    + (boundvalue & 3)].
     * @exception IndexOutOfBoundsException if offset16 is not within the
     *                                      range of start and limit.
     * @stable ICU 2.1
     */
    public static int bounds(char source[], int start, int limit,
                             int offset16)
    {
        offset16 += start;
        if (offset16 < start || offset16 >= limit) {
            throw new ArrayIndexOutOfBoundsException(offset16);
        }
        char ch = source[offset16];
        if (isSurrogate(ch)) {
            if (isLeadSurrogate(ch)) {
                ++ offset16;
                if (offset16 < limit && isTrailSurrogate(source[offset16])) {
                    return LEAD_SURROGATE_BOUNDARY;
                }
            }
            else { // isTrailSurrogate(ch), so
                -- offset16;
                if (offset16 >= start && isLeadSurrogate(source[offset16])) {
                    return TRAIL_SURROGATE_BOUNDARY;
                }
            }
        }
        return SINGLE_CHAR_BOUNDARY;
    }

    /**
     * Determines whether the code value is a surrogate.
     * @param char16 the input character.
     * @return true iff the input character is a surrogate.
     * @stable ICU 2.1
     */
    public static boolean isSurrogate(char char16)
    {
        return LEAD_SURROGATE_MIN_VALUE <= char16 &&
            char16 <= TRAIL_SURROGATE_MAX_VALUE;
    }

    /**
     * Determines whether the character is a trail surrogate.
     * @param char16 the input character.
     * @return true iff the input character is a trail surrogate.
     * @stable ICU 2.1
     */
    public static boolean isTrailSurrogate(char char16)
    {
        return (TRAIL_SURROGATE_MIN_VALUE <= char16 &&
                char16 <= TRAIL_SURROGATE_MAX_VALUE);
    }

    /**
     * Determines whether the character is a lead surrogate.
     * @param char16 the input character.
     * @return true iff the input character is a lead surrogate
     * @stable ICU 2.1
     */
    public static boolean isLeadSurrogate(char char16)
    {
        return LEAD_SURROGATE_MIN_VALUE <= char16 &&
            char16 <= LEAD_SURROGATE_MAX_VALUE;
    }

    /**
     * Returns the lead surrogate.
     * If a validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code>
     * on char32 before calling.
     * @param char32 the input character.
     * @return lead surrogate if the getCharCount(ch) is 2; <br>
     *         and 0 otherwise (note: 0 is not a valid lead surrogate).
     * @stable ICU 2.1
     */
    public static char getLeadSurrogate(int char32)
    {
        if (char32 >= SUPPLEMENTARY_MIN_VALUE) {
            return (char)(LEAD_SURROGATE_OFFSET_ +
                          (char32 >> LEAD_SURROGATE_SHIFT_));
        }

        return 0;
    }

    /**
     * Returns the trail surrogate.
     * If a validity check is required, use
     * <code><a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code>
     * on char32 before calling.
     * @param char32 the input character.
     * @return the trail surrogate if the getCharCount(ch) is 2; <br>otherwise
     *         the character itself
     * @stable ICU 2.1
     */
    public static char getTrailSurrogate(int char32)
    {
        if (char32 >= SUPPLEMENTARY_MIN_VALUE) {
            return (char)(TRAIL_SURROGATE_MIN_VALUE +
                          (char32 & TRAIL_SURROGATE_MASK_));
        }

        return (char)char32;
    }

    /**
     * Convenience method corresponding to String.valueOf(char). Returns a one
     * or two char string containing the UTF-32 value in UTF16 format. If a
     * validity check is required, use
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on
     * char32 before calling.
     * @param char32 the input character.
     * @return string value of char32 in UTF16 format
     * @exception IllegalArgumentException thrown if char32 is a invalid
     *            codepoint.
     * @stable ICU 2.1
     */
    public static String valueOf(int char32)
    {
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException("Illegal codepoint");
        }
        return toString(char32);
    }

    /**
     * Convenience method corresponding to String.valueOf(codepoint at
     * offset16).
     * Returns a one or two char string containing the UTF-32 value in UTF16
     * format. If offset16 indexes a surrogate character, the whole
     * supplementary codepoint will be returned.
     * If a validity check is required, use
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on the
     * codepoint at offset16 before calling.
     * The result returned will be a newly created String obtained by calling
     * source.substring(..) with the appropriate indexes.
     * @param source the input string.
     * @param offset16 the UTF16 index to the codepoint in source
     * @return string value of char32 in UTF16 format
     * @stable ICU 2.1
     */
    public static String valueOf(String source, int offset16)
    {
        switch (bounds(source, offset16)) {
        case LEAD_SURROGATE_BOUNDARY:
            return source.substring(offset16, offset16 + 2);
        case TRAIL_SURROGATE_BOUNDARY:
            return source.substring(offset16 - 1, offset16 + 1);
        default: return source.substring(offset16, offset16 + 1);
        }
    }

    /**
     * Convenience method corresponding to
     * StringBuffer.valueOf(codepoint at offset16).
     * Returns a one or two char string containing the UTF-32 value in UTF16
     * format. If offset16 indexes a surrogate character, the whole
     * supplementary codepoint will be returned.
     * If a validity check is required, use
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on the
     * codepoint at offset16 before calling.
     * The result returned will be a newly created String obtained by calling
     * source.substring(..) with the appropriate indexes.
     * @param source the input string buffer.
     * @param offset16 the UTF16 index to the codepoint in source
     * @return string value of char32 in UTF16 format
     * @stable ICU 2.1
     */
    public static String valueOf(StringBuffer source, int offset16)
    {
        switch (bounds(source, offset16)) {
        case LEAD_SURROGATE_BOUNDARY:
            return source.substring(offset16, offset16 + 2);
        case TRAIL_SURROGATE_BOUNDARY:
            return source.substring(offset16 - 1, offset16 + 1);
        default: return source.substring(offset16, offset16 + 1);
        }
    }

    /**
     * Convenience method.
     * Returns a one or two char string containing the UTF-32 value in UTF16
     * format. If offset16 indexes a surrogate character, the whole
     * supplementary codepoint will be returned, except when either the
     * leading or trailing surrogate character lies out of the specified
     * subarray. In the latter case, only the surrogate character within
     * bounds will be returned.
     * If a validity check is required, use
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on the
     * codepoint at offset16 before calling.
     * The result returned will be a newly created String containing the
     * relevant characters.
     * @param source the input char array.
     * @param start start index of the subarray
     * @param limit end index of the subarray
     * @param offset16 the UTF16 index to the codepoint in source relative to
     *        start
     * @return string value of char32 in UTF16 format
     * @stable ICU 2.1
     */
    public static String valueOf(char source[], int start, int limit,
                                 int offset16)
    {
        switch (bounds(source, start, limit, offset16)) {
        case LEAD_SURROGATE_BOUNDARY:
            return new String(source, start + offset16, 2);
        case TRAIL_SURROGATE_BOUNDARY:
            return new String(source, start + offset16 - 1, 2);
        }
        return new String(source, start + offset16, 1);
    }

    /**
     * Returns the UTF-16 offset that corresponds to a UTF-32 offset.
     * Used for random access. See the <a name="_top_">class description</a>
     * for notes on roundtripping.
     * @param source the UTF-16 string
     * @param offset32 UTF-32 offset
     * @return UTF-16 offset
     * @exception IndexOutOfBoundsException if offset32 is out of bounds.
     * @stable ICU 2.1
     */
    public static int findOffsetFromCodePoint(String source, int offset32)
    {
        char ch;
        int size = source.length(),
            result = 0,
            count = offset32;
        if (offset32 < 0 || offset32 > size) {
            throw new StringIndexOutOfBoundsException(offset32);
        }
        while (result < size && count > 0)
            {
                ch = source.charAt(result);
                if (isLeadSurrogate(ch) && ((result + 1) < size) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    result ++;
                }

                count --;
                result ++;
            }
        if (count != 0) {
            throw new StringIndexOutOfBoundsException(offset32);
        }
        return result;
    }

    /**
     * Returns the UTF-16 offset that corresponds to a UTF-32 offset.
     * Used for random access. See the <a name="_top_">class description</a>
     * for notes on roundtripping.
     * @param source the UTF-16 string buffer
     * @param offset32 UTF-32 offset
     * @return UTF-16 offset
     * @exception IndexOutOfBoundsException if offset32 is out of bounds.
     * @stable ICU 2.1
     */
    public static int findOffsetFromCodePoint(StringBuffer source,
                                              int offset32)
    {
        char ch;
        int size = source.length(),
            result = 0,
            count = offset32;
        if (offset32 < 0 || offset32 > size) {
            throw new StringIndexOutOfBoundsException(offset32);
        }
        while (result < size && count > 0)
            {
                ch = source.charAt(result);
                if (isLeadSurrogate(ch) && ((result + 1) < size) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    result ++;
                }

                count --;
                result ++;
            }
        if (count != 0) {
            throw new StringIndexOutOfBoundsException(offset32);
        }
        return result;
    }

    /**
     * Returns the UTF-16 offset that corresponds to a UTF-32 offset.
     * Used for random access. See the <a name="_top_">class description</a>
     * for notes on roundtripping.
     * @param source the UTF-16 char array whose substring is to be analysed
     * @param start offset of the substring to be analysed
     * @param limit offset of the substring to be analysed
     * @param offset32 UTF-32 offset relative to start
     * @return UTF-16 offset relative to start
     * @exception IndexOutOfBoundsException if offset32 is out of bounds.
     * @stable ICU 2.1
     */
    public static int findOffsetFromCodePoint(char source[], int start,
                                              int limit, int offset32)
    {
        char ch;
        int result = start,
            count = offset32;
        if (offset32 > limit - start) {
            throw new ArrayIndexOutOfBoundsException(offset32);
        }
        while (result < limit && count > 0)
            {
                ch = source[result];
                if (isLeadSurrogate(ch) && ((result + 1) < limit) &&
                    isTrailSurrogate(source[result + 1])) {
                    result ++;
                }

                count --;
                result ++;
            }
        if (count != 0) {
            throw new ArrayIndexOutOfBoundsException(offset32);
        }
        return result - start;
    }

    /**
     * Returns the UTF-32 offset corresponding to the first UTF-32 boundary at
     * or after the given UTF-16 offset. Used for random access. See the
     * <a name="_top_">class description</a> for notes on roundtripping.<br>
     * <i>Note: If the UTF-16 offset is into the middle of a surrogate pair,
     * then the UTF-32 offset of the <strong>lead</strong> of the pair is
     * returned.
     * </i>
     * <p>
     * To find the UTF-32 length of a string, use:
     *   <pre>
     *     len32 = countCodePoint(source, source.length());
     *   </pre>
     * </p>
     * <p>
     * @param source text to analyse
     * @param offset16 UTF-16 offset < source text length.
     * @return UTF-32 offset
     * @exception IndexOutOfBoundsException if offset16 is out of bounds.
     * @stable ICU 2.1
     */
    public static int findCodePointOffset(String source, int offset16)
    {
        if (offset16 < 0 || offset16 > source.length()) {
            throw new StringIndexOutOfBoundsException(offset16);
        }

        int result = 0;
        char ch;
        boolean hadLeadSurrogate = false;

        for (int i = 0; i < offset16; ++ i)
            {
                ch = source.charAt(i);
                if (hadLeadSurrogate && isTrailSurrogate(ch)) {
                    hadLeadSurrogate = false;           // count valid trail as zero
                }
                else
                    {
                        hadLeadSurrogate = isLeadSurrogate(ch);
                        ++ result;                          // count others as 1
                    }
            }

        if (offset16 == source.length()) {
            return result;
        }

        // end of source being the less significant surrogate character
        // shift result back to the start of the supplementary character
        if (hadLeadSurrogate && (isTrailSurrogate(source.charAt(offset16)))) {
            result --;
        }

        return result;
    }

    /**
     * Returns the UTF-32 offset corresponding to the first UTF-32 boundary at
     * the given UTF-16 offset. Used for random access. See the
     * <a name="_top_">class description</a> for notes on roundtripping.<br>
     * <i>Note: If the UTF-16 offset is into the middle of a surrogate pair,
     * then the UTF-32 offset of the <strong>lead</strong> of the pair is
     * returned.
     * </i>
     * <p>
     * To find the UTF-32 length of a string, use:
     *   <pre>
     *     len32 = countCodePoint(source);
     *   </pre>
     * </p>
     * <p>
     * @param source text to analyse
     * @param offset16 UTF-16 offset < source text length.
     * @return UTF-32 offset
     * @exception IndexOutOfBoundsException if offset16 is out of bounds.
     * @stable ICU 2.1
     */
    public static int findCodePointOffset(StringBuffer source, int offset16)
    {
        if (offset16 < 0 || offset16 > source.length()) {
            throw new StringIndexOutOfBoundsException(offset16);
        }

        int result = 0;
        char ch;
        boolean hadLeadSurrogate = false;

        for (int i = 0; i < offset16; ++ i)
            {
                ch = source.charAt(i);
                if (hadLeadSurrogate && isTrailSurrogate(ch)) {
                    hadLeadSurrogate = false;           // count valid trail as zero
                }
                else
                    {
                        hadLeadSurrogate = isLeadSurrogate(ch);
                        ++ result;                          // count others as 1
                    }
            }

        if (offset16 == source.length()) {
            return result;
        }

        // end of source being the less significant surrogate character
        // shift result back to the start of the supplementary character
        if (hadLeadSurrogate && (isTrailSurrogate(source.charAt(offset16))))
            {
                result --;
            }

        return result;
    }

    /**
     * Returns the UTF-32 offset corresponding to the first UTF-32 boundary at
     * the given UTF-16 offset. Used for random access. See the
     * <a name="_top_">class description</a> for notes on roundtripping.<br>
     * <i>Note: If the UTF-16 offset is into the middle of a surrogate pair,
     * then the UTF-32 offset of the <strong>lead</strong> of the pair is
     * returned.
     * </i>
     * <p>
     * To find the UTF-32 length of a substring, use:
     *   <pre>
     *     len32 = countCodePoint(source, start, limit);
     *   </pre>
     * </p>
     * <p>
     * @param source text to analyse
     * @param start offset of the substring
     * @param limit offset of the substring
     * @param offset16 UTF-16 relative to start
     * @return UTF-32 offset relative to start
     * @exception IndexOutOfBoundsException if offset16 is not within the
     *            range of start and limit.
     * @stable ICU 2.1
     */
    public static int findCodePointOffset(char source[], int start, int limit,
                                          int offset16)
    {
        offset16 += start;
        if (offset16 > limit) {
            throw new StringIndexOutOfBoundsException(offset16);
        }

        int result = 0;
        char ch;
        boolean hadLeadSurrogate = false;

        for (int i = start; i < offset16; ++ i)
            {
                ch = source[i];
                if (hadLeadSurrogate && isTrailSurrogate(ch)) {
                    hadLeadSurrogate = false; // count valid trail as zero
                }
                else
                    {
                        hadLeadSurrogate = isLeadSurrogate(ch);
                        ++ result;                          // count others as 1
                    }
            }

        if (offset16 == limit) {
            return result;
        }

        // end of source being the less significant surrogate character
        // shift result back to the start of the supplementary character
        if (hadLeadSurrogate && (isTrailSurrogate(source[offset16]))) {
            result --;
        }

        return result;
    }

    /**
     * Append a single UTF-32 value to the end of a StringBuffer.
     * If a validity check is required, use
     * <a href="../lang/UCharacter.html#isLegal(char)">isLegal()</a></code> on
     * char32 before calling.
     * @param target the buffer to append to
     * @param char32 value to append.
     * @return the updated StringBuffer
     * @exception IllegalArgumentException thrown when char32 does not lie
     *            within the range of the Unicode codepoints
     * @stable ICU 2.1
     */
    public static StringBuffer append(StringBuffer target, int char32)
    {
        // Check for irregular values
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException("Illegal codepoint: " + Integer.toHexString(char32));
        }

        // Write the UTF-16 values
        if (char32 >= SUPPLEMENTARY_MIN_VALUE)
            {
                target.append(getLeadSurrogate(char32));
                target.append(getTrailSurrogate(char32));
            }
        else {
            target.append((char)char32);
        }
        return target;
    }

    /**
     * Cover JDK 1.5 APIs.  Append the code point to the buffer and return the buffer
     * as a convenience.
     *
     * @param target the buffer to append to
     * @param cp the code point to append
     * @return the updated StringBuffer
     * @throws IllegalArgumentException if cp is not a valid code point
     * @draft ICU 3.0
     * @provisional This API might change or be removed in a future release.
     */
    public static StringBuffer appendCodePoint(StringBuffer target, int cp) {
        return append(target, cp);
    }

    /**
     * Adds a codepoint to offset16 position of the argument char array.
     * @param target char array to be append with the new code point
     * @param limit UTF16 offset which the codepoint will be appended.
     * @param char32 code point to be appended
     * @return offset after char32 in the array.
     * @exception IllegalArgumentException thrown if there is not enough
     *            space for the append, or when char32 does not lie within
     *            the range of the Unicode codepoints.
     * @stable ICU 2.1
     */
    public static int append(char[] target, int limit, int char32)
    {
        // Check for irregular values
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException("Illegal codepoint");
        }
        // Write the UTF-16 values
        if (char32 >= SUPPLEMENTARY_MIN_VALUE)
            {
                target[limit ++] = getLeadSurrogate(char32);
                target[limit ++] = getTrailSurrogate(char32);
            }
        else {
            target[limit ++] = (char)char32;
        }
        return limit;
    }

    /**
     * Number of codepoints in a UTF16 String
     * @param source UTF16 string
     * @return number of codepoint in string
     * @stable ICU 2.1
     */
    public static int countCodePoint(String source)
    {
        if (source == null || source.length() == 0) {
            return 0;
        }
        return findCodePointOffset(source, source.length());
    }

    /**
     * Number of codepoints in a UTF16 String buffer
     * @param source UTF16 string buffer
     * @return number of codepoint in string
     * @stable ICU 2.1
     */
    public static int countCodePoint(StringBuffer source)
    {
        if (source == null || source.length() == 0) {
            return 0;
        }
        return findCodePointOffset(source, source.length());
    }

    /**
     * Number of codepoints in a UTF16 char array substring
     * @param source UTF16 char array
     * @param start offset of the substring
     * @param limit offset of the substring
     * @return number of codepoint in the substring
     * @exception IndexOutOfBoundsException if start and limit are not valid.
     * @stable ICU 2.1
     */
    public static int countCodePoint(char source[], int start, int limit)
    {
        if (source == null || source.length == 0) {
            return 0;
        }
        return findCodePointOffset(source, start, limit, limit - start);
    }

    /**
     * Set a code point into a UTF16 position.
     * Adjusts target according if we are replacing a non-supplementary
     * codepoint with a supplementary and vice versa.
     * @param target stringbuffer
     * @param offset16 UTF16 position to insert into
     * @param char32 code point
     * @stable ICU 2.1
     */
    public static void setCharAt(StringBuffer target, int offset16,
                                 int char32)
    {
        int count = 1;
        char single = target.charAt(offset16);

        if (isSurrogate(single))
            {
                // pairs of the surrogate with offset16 at the lead char found
                if (isLeadSurrogate(single) && (target.length() > offset16 + 1)
                    && isTrailSurrogate(target.charAt(offset16 + 1))) {
                    count ++;
                }
                else {
                    // pairs of the surrogate with offset16 at the trail char
                    // found
                    if (isTrailSurrogate(single) && (offset16 > 0) &&
                        isLeadSurrogate(target.charAt(offset16 -1)))
                        {
                            offset16 --;
                            count ++;
                        }
                }
            }
        target.replace(offset16, offset16 + count, valueOf(char32));
    }

    /**
     * Set a code point into a UTF16 position in a char array.
     * Adjusts target according if we are replacing a non-supplementary
     * codepoint with a supplementary and vice versa.
     * @param target char array
     * @param limit numbers of valid chars in target, different from
     *        target.length. limit counts the number of chars in target
     *        that represents a string, not the size of array target.
     * @param offset16 UTF16 position to insert into
     * @param char32 code point
     * @return new number of chars in target that represents a string
     * @exception IndexOutOfBoundsException if offset16 is out of range
     * @stable ICU 2.1
     */
    public static int setCharAt(char target[], int limit,
                                int offset16, int char32)
    {
        if (offset16 >= limit) {
            throw new ArrayIndexOutOfBoundsException(offset16);
        }
        int count = 1;
        char single = target[offset16];

        if (isSurrogate(single))
            {
                // pairs of the surrogate with offset16 at the lead char found
                if (isLeadSurrogate(single) && (target.length > offset16 + 1) &&
                    isTrailSurrogate(target[offset16 + 1])) {
                    count ++;
                }
                else {
                    // pairs of the surrogate with offset16 at the trail char
                    // found
                    if (isTrailSurrogate(single) && (offset16 > 0) &&
                        isLeadSurrogate(target[offset16 -1]))
                        {
                            offset16 --;
                            count ++;
                        }
                }
            }

        String str = valueOf(char32);
        int result = limit;
        int strlength = str.length();
        target[offset16] = str.charAt(0);
        if (count == strlength) {
            if (count == 2) {
                target[offset16 + 1] = str.charAt(1);
            }
        }
        else {
            // this is not exact match in space, we'll have to do some
            // shifting
            System.arraycopy(target, offset16 + count, target,
                             offset16 + strlength, limit - (offset16 + count));
            if (count < strlength) {
                // char32 is a supplementary character trying to squeeze into
                // a non-supplementary space
                target[offset16 + 1] = str.charAt(1);
                result ++;
                if (result < target.length) {
                    target[result] = 0;
                }
            }
            else {
                // char32 is a non-supplementary character trying to fill
                // into a supplementary space
                result --;
                target[result] = 0;
            }
        }
        return result;
    }

    /**
     * Shifts offset16 by the argument number of codepoints
     * @param source string
     * @param offset16 UTF16 position to shift
     * @param shift32 number of codepoints to shift
     * @return new shifted offset16
     * @exception IndexOutOfBoundsException if the new offset16 is out of
     *                                      bounds.
     * @stable ICU 2.1
     */
    public static int moveCodePointOffset(String source, int offset16,
                                          int shift32)
    {
        int result = offset16;
        int size = source.length();
        int count;
        char ch;
        if (offset16<0 || offset16>size) {
            throw new StringIndexOutOfBoundsException(offset16);
        }
        if (shift32 > 0 ) {
            if (shift32 + offset16 > size) {
                throw new StringIndexOutOfBoundsException(offset16);
            }
            count = shift32;
            while (result < size && count > 0)
            {
                ch = source.charAt(result);
                if (isLeadSurrogate(ch) && ((result + 1) < size) &&
                        isTrailSurrogate(source.charAt(result + 1))) {
                    result ++;
                }
                count --;
                result ++;
            }
        } else {
            if (offset16 + shift32 < 0) {
                throw new StringIndexOutOfBoundsException(offset16);
            }
            for (count=-shift32; count>0; count--) {
                result--;
                if (result<0) {
                    break;
                }
                ch = source.charAt(result);
                if (isTrailSurrogate(ch) && result>0 && isLeadSurrogate(source.charAt(result-1))) {
                    result--;
                }
            }
        }
        if (count != 0)  {
            throw new StringIndexOutOfBoundsException(shift32);
        }
        return result;
    }

    /**
     * Shifts offset16 by the argument number of codepoints
     * @param source string buffer
     * @param offset16 UTF16 position to shift
     * @param shift32 number of codepoints to shift
     * @return new shifted offset16
     * @exception IndexOutOfBoundsException if the new offset16 is out of
     *                                      bounds.
     * @stable ICU 2.1
     */
    public static int moveCodePointOffset(StringBuffer source, int offset16,
                                          int shift32)
    {
        int result = offset16;
        int size = source.length();
        int count;
        char ch;
        if (offset16<0 || offset16>size) {
            throw new StringIndexOutOfBoundsException(offset16);
        }
        if (shift32 > 0 ) {
            if (shift32 + offset16 > size) {
                throw new StringIndexOutOfBoundsException(offset16);
            }
            count = shift32;
            while (result < size && count > 0)
            {
                ch = source.charAt(result);
                if (isLeadSurrogate(ch) && ((result + 1) < size) &&
                        isTrailSurrogate(source.charAt(result + 1))) {
                    result ++;
                }
                count --;
                result ++;
            }
        } else {
            if (offset16 + shift32 < 0) {
                throw new StringIndexOutOfBoundsException(offset16);
            }
            for (count=-shift32; count>0; count--) {
                result--;
                if (result<0) {
                    break;
                }
                ch = source.charAt(result);
                if (isTrailSurrogate(ch) && result>0 && isLeadSurrogate(source.charAt(result-1))) {
                    result--;
                }
            }
        }
        if (count != 0)  {
            throw new StringIndexOutOfBoundsException(shift32);
        }
        return result;
    }

    /**
     * Shifts offset16 by the argument number of codepoints within a subarray.
     * @param source char array
     * @param start position of the subarray to be performed on
     * @param limit position of the subarray to be performed on
     * @param offset16 UTF16 position to shift relative to start
     * @param shift32 number of codepoints to shift
     * @return new shifted offset16 relative to start
     * @exception IndexOutOfBoundsException if the new offset16 is out of
     *            bounds with respect to the subarray or the subarray bounds
     *            are out of range.
     * @stable ICU 2.1
     */
    public static int moveCodePointOffset(char source[], int start, int limit,
                                          int offset16, int shift32)
    {
        int         size = source.length;
        int         count;
        char        ch;
        int         result = offset16 + start;
        if (start<0 || limit<start) {
            throw new StringIndexOutOfBoundsException(start);
        }
        if (limit>size) {
            throw new StringIndexOutOfBoundsException(limit);
        }
        if (offset16<0 || result>limit) {
            throw new StringIndexOutOfBoundsException(offset16);
        }
        if (shift32 > 0 ) {
            if (shift32 + result > size) {
                throw new StringIndexOutOfBoundsException(result);
            }
            count = shift32;
            while (result < limit && count > 0)
            {
                ch = source[result];
                if (isLeadSurrogate(ch) && (result+1 < limit) &&
                        isTrailSurrogate(source[result+1])) {
                    result ++;
                }
                count --;
                result ++;
            }
        } else {
            if (result + shift32 < start) {
                throw new StringIndexOutOfBoundsException(result);
            }
            for (count=-shift32; count>0; count--) {
                result--;
                if (result<start) {
                    break;
                }
                ch = source[result];
                if (isTrailSurrogate(ch) && result>start && isLeadSurrogate(source[result-1])) {
                    result--;
                }
            }
        }
        if (count != 0)  {
            throw new StringIndexOutOfBoundsException(shift32);
        }
        result -= start;
        return result;
    }

    /**
     * Inserts char32 codepoint into target at the argument offset16.
     * If the offset16 is in the middle of a supplementary codepoint, char32
     * will be inserted after the supplementary codepoint.
     * The length of target increases by one if codepoint is non-supplementary,
     * 2 otherwise.
     * <p>
     * The overall effect is exactly as if the argument were converted to a
     * string by the method valueOf(char) and the characters in that string
     * were then inserted into target at the position indicated by offset16.
     * </p>
     * <p>
     * The offset argument must be greater than or equal to 0, and less than
     * or equal to the length of source.
     * @param target string buffer to insert to
     * @param offset16 offset which char32 will be inserted in
     * @param char32 codepoint to be inserted
     * @return a reference to target
     * @exception IndexOutOfBoundsException thrown if offset16 is invalid.
     * @stable ICU 2.1
     */
    public static StringBuffer insert(StringBuffer target, int offset16,
                                      int char32)
    {
        String str = valueOf(char32);
        if (offset16 != target.length() &&
            bounds(target, offset16) == TRAIL_SURROGATE_BOUNDARY) {
            offset16 ++;
        }
        target.insert(offset16, str);
        return target;
    }

    /**
     * Inserts char32 codepoint into target at the argument offset16.
     * If the offset16 is in the middle of a supplementary codepoint, char32
     * will be inserted after the supplementary codepoint.
     * Limit increases by one if codepoint is non-supplementary, 2 otherwise.
     * <p>
     * The overall effect is exactly as if the argument were converted to a
     * string by the method valueOf(char) and the characters in that string
     * were then inserted into target at the position indicated by offset16.
     * </p>
     * <p>
     * The offset argument must be greater than or equal to 0, and less than
     * or equal to the limit.
     * @param target char array to insert to
     * @param limit end index of the char array, limit <= target.length
     * @param offset16 offset which char32 will be inserted in
     * @param char32 codepoint to be inserted
     * @return new limit size
     * @exception IndexOutOfBoundsException thrown if offset16 is invalid.
     * @stable ICU 2.1
     */
    public static int insert(char target[], int limit, int offset16,
                             int char32)
    {
        String str = valueOf(char32);
        if (offset16 != limit &&
            bounds(target, 0, limit, offset16) == TRAIL_SURROGATE_BOUNDARY) {
            offset16 ++;
        }
        int size = str.length();
        if (limit + size > target.length) {
            throw new ArrayIndexOutOfBoundsException(offset16 + size);
        }
        System.arraycopy(target, offset16, target, offset16 + size,
                         limit - offset16);
        target[offset16] = str.charAt(0);
        if (size == 2) {
            target[offset16 + 1] = str.charAt(1);
        }
        return limit + size;
    }

    /**
     * Removes the codepoint at the specified position in this target
     * (shortening target by 1 character if the codepoint is a
     * non-supplementary, 2 otherwise).
     * @param target string buffer to remove codepoint from
     * @param offset16 offset which the codepoint will be removed
     * @return a reference to target
     * @exception IndexOutOfBoundsException thrown if offset16 is invalid.
     * @stable ICU 2.1
     */
    public static StringBuffer delete(StringBuffer target, int offset16)
    {
        int count = 1;
        switch (bounds(target, offset16)) {
        case LEAD_SURROGATE_BOUNDARY:
            count ++;
            break;
        case TRAIL_SURROGATE_BOUNDARY:
            count ++;
            offset16 --;
            break;
        }
        target.delete(offset16, offset16 + count);
        return target;
    }

    /**
     * Removes the codepoint at the specified position in this target
     * (shortening target by 1 character if the codepoint is a
     * non-supplementary, 2 otherwise).
     * @param target string buffer to remove codepoint from
     * @param limit end index of the char array, limit <= target.length
     * @param offset16 offset which the codepoint will be removed
     * @return a new limit size
     * @exception IndexOutOfBoundsException thrown if offset16 is invalid.
     * @stable ICU 2.1
     */
    public static int delete(char target[], int limit, int offset16)
    {
        int count = 1;
        switch (bounds(target, 0, limit, offset16)) {
        case LEAD_SURROGATE_BOUNDARY:
            count ++;
            break;
        case TRAIL_SURROGATE_BOUNDARY:
            count ++;
            offset16 --;
            break;
        }
        System.arraycopy(target, offset16 + count, target, offset16,
                         limit - (offset16 + count));
        target[limit - count] = 0;
        return limit - count;
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the first occurrence of the argument codepoint. I.e., the smallest
     * index <code>i</code> such that <code>UTF16.charAt(source, i) ==
     * char32</code> is true.
     * <p>If no such character occurs in this string, then -1 is returned.</p>
     * <p>
     * Examples:<br>
     * UTF16.indexOf("abc", 'a') returns 0<br>
     * UTF16.indexOf("abc\ud800\udc00", 0x10000) returns 3<br>
     * UTF16.indexOf("abc\ud800\udc00", 0xd800) returns -1<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param char32 codepoint to search for
     * @return the index of the first occurrence of the codepoint in the
     *         argument Unicode string, or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int indexOf(String source, int char32)
    {
        if (char32 < CODEPOINT_MIN_VALUE ||
            char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument char32 is not a valid codepoint");
        }
        // non-surrogate bmp
        if (char32 < LEAD_SURROGATE_MIN_VALUE ||
            (char32 > TRAIL_SURROGATE_MAX_VALUE &&
             char32 < SUPPLEMENTARY_MIN_VALUE)) {
            return source.indexOf((char)char32);
        }
        // surrogate
        if (char32 < SUPPLEMENTARY_MIN_VALUE) {
            int result = source.indexOf((char)char32);
            if (result >= 0) {
                if (isLeadSurrogate((char)char32) &&
                    (result < source.length() - 1) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    return indexOf(source, char32, result + 1);
                }
                // trail surrogate
                if (result > 0 &&
                    isLeadSurrogate(source.charAt(result - 1))) {
                    return indexOf(source, char32, result + 1);
                }
            }
            return result;
        }
        // supplementary
        String char32str = toString(char32);
        return source.indexOf(char32str);
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the first occurrence of the argument string str. This method is
     * implemented based on codepoints, hence a "lead surrogate character +
     * trail surrogate character" is treated as one entity.e
     * Hence if the str starts with trail surrogate character at index 0, a
     * source with a leading a surrogate character before str found at in
     * source will not have a valid match. Vice versa for lead surrogates
     * that ends str.
     * See example below.
     * <p>If no such string str occurs in this source, then -1 is returned.
     * </p> <p>
     * Examples:<br>
     * UTF16.indexOf("abc", "ab") returns 0<br>
     * UTF16.indexOf("abc\ud800\udc00", "\ud800\udc00") returns 3<br>
     * UTF16.indexOf("abc\ud800\udc00", "\ud800") returns -1<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param str UTF16 format Unicode string to search for
     * @return the index of the first occurrence of the codepoint in the
     *         argument Unicode string, or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int indexOf(String source, String str)
    {
        int strLength = str.length();
        // non-surrogate ends
        if (!isTrailSurrogate(str.charAt(0)) &&
            !isLeadSurrogate(str.charAt(strLength - 1))) {
            return source.indexOf(str);
        }

        int result    = source.indexOf(str);
        int resultEnd = result + strLength;
        if (result >= 0) {
            // check last character
            if (isLeadSurrogate(str.charAt(strLength - 1)) &&
                (result < source.length() - 1) &&
                isTrailSurrogate(source.charAt(resultEnd + 1))) {
                return indexOf(source, str, resultEnd + 1);
            }
            // check first character which is a trail surrogate
            if (isTrailSurrogate(str.charAt(0)) && result > 0 &&
                isLeadSurrogate(source.charAt(result - 1))) {
                return indexOf(source, str, resultEnd + 1);
            }
        }
        return result;
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the first occurrence of the argument codepoint. I.e., the smallest
     * index i such that: <br>
     * (UTF16.charAt(source, i) == char32 && i >= fromIndex) is true.
     * <p>If no such character occurs in this string, then -1 is returned.</p>
     * <p>
     * Examples:<br>
     * UTF16.indexOf("abc", 'a', 1) returns -1<br>
     * UTF16.indexOf("abc\ud800\udc00", 0x10000, 1) returns 3<br>
     * UTF16.indexOf("abc\ud800\udc00", 0xd800, 1) returns -1<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param char32 codepoint to search for
     * @param fromIndex the index to start the search from.
     * @return the index of the first occurrence of the codepoint in the
     *         argument Unicode string at or after fromIndex, or -1 if the
     *         codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int indexOf(String source, int char32, int fromIndex)
    {
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument char32 is not a valid codepoint");
        }
        // non-surrogate bmp
        if (char32 < LEAD_SURROGATE_MIN_VALUE ||
            (char32 > TRAIL_SURROGATE_MAX_VALUE &&
             char32 < SUPPLEMENTARY_MIN_VALUE)) {
            return source.indexOf((char)char32, fromIndex);
        }
        // surrogate
        if (char32 < SUPPLEMENTARY_MIN_VALUE) {
            int result = source.indexOf((char)char32, fromIndex);
            if (result >= 0) {
                if (isLeadSurrogate((char)char32) &&
                    (result < source.length() - 1) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    return indexOf(source, char32, result + 1);
                }
                // trail surrogate
                if (result > 0 &&
                    isLeadSurrogate(source.charAt(result - 1))) {
                    return indexOf(source, char32, result + 1);
                }
            }
            return result;
        }
        // supplementary
        String char32str = toString(char32);
        return source.indexOf(char32str, fromIndex);
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the first occurrence of the argument string str. This method is
     * implemented based on codepoints, hence a "lead surrogate character +
     * trail surrogate character" is treated as one entity.e
     * Hence if the str starts with trail surrogate character at index 0, a
     * source with a leading a surrogate character before str found at in
     * source will not have a valid match. Vice versa for lead surrogates
     * that ends str.
     * See example below.
     * <p>If no such string str occurs in this source, then -1 is returned.
     * </p> <p>
     * Examples:<br>
     * UTF16.indexOf("abc", "ab", 0) returns 0<br>
     * UTF16.indexOf("abc\ud800\udc00", "\ud800\udc00", 0) returns 3<br>
     * UTF16.indexOf("abc\ud800\udc00", "\ud800\udc00", 2) returns 3<br>
     * UTF16.indexOf("abc\ud800\udc00", "\ud800", 0) returns -1<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param str UTF16 format Unicode string to search for
     * @param fromIndex the index to start the search from.
     * @return the index of the first occurrence of the codepoint in the
     *         argument Unicode string, or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int indexOf(String source, String str, int fromIndex)
    {
        int strLength = str.length();
        // non-surrogate ends
        if (!isTrailSurrogate(str.charAt(0)) &&
            !isLeadSurrogate(str.charAt(strLength - 1))) {
            return source.indexOf(str, fromIndex);
        }

        int result    = source.indexOf(str, fromIndex);
        int resultEnd = result + strLength;
        if (result >= 0) {
            // check last character
            if (isLeadSurrogate(str.charAt(strLength - 1)) &&
                (result < source.length() - 1) &&
                isTrailSurrogate(source.charAt(resultEnd))) {
                return indexOf(source, str, resultEnd + 1);
            }
            // check first character which is a trail surrogate
            if (isTrailSurrogate(str.charAt(0)) && result > 0 &&
                isLeadSurrogate(source.charAt(result - 1))) {
                return indexOf(source, str, resultEnd + 1);
            }
        }
        return result;
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the last occurrence of the argument codepoint. I.e., the index returned
     * is the largest value i such that: UTF16.charAt(source, i) == char32
     * is true.
     * <p>
     * Examples:<br>
     * UTF16.lastIndexOf("abc", 'a') returns 0<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", 0x10000) returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", 0xd800) returns -1<br>
     * </p>
     * <p>source is searched backwards starting at the last character.</p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param char32 codepoint to search for
     * @return the index of the last occurrence of the codepoint in source,
     *         or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int lastIndexOf(String source, int char32)
    {
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument char32 is not a valid codepoint");
        }
        // non-surrogate bmp
        if (char32 < LEAD_SURROGATE_MIN_VALUE ||
            (char32 > TRAIL_SURROGATE_MAX_VALUE &&
             char32 < SUPPLEMENTARY_MIN_VALUE)) {
            return source.lastIndexOf((char)char32);
        }
        // surrogate
        if (char32 < SUPPLEMENTARY_MIN_VALUE) {
            int result = source.lastIndexOf((char)char32);
            if (result >= 0) {
                if (isLeadSurrogate((char)char32) &&
                    (result < source.length() - 1) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    return lastIndexOf(source, char32, result - 1);
                }
                // trail surrogate
                if (result > 0 &&
                    isLeadSurrogate(source.charAt(result - 1))) {
                    return lastIndexOf(source, char32, result - 1);
                }
            }
            return result;
        }
        // supplementary
        String char32str = toString(char32);
        return source.lastIndexOf(char32str);
    }

    /**
     * Returns the index within the argument UTF16 format Unicode string of
     * the last occurrence of the argument string str. This method is
     * implemented based on codepoints, hence a "lead surrogate character +
     * trail surrogate character" is treated as one entity.e
     * Hence if the str starts with trail surrogate character at index 0, a
     * source with a leading a surrogate character before str found at in
     * source will not have a valid match. Vice versa for lead surrogates
     * that ends str.
     * See example below.
     * <p>
     * Examples:<br>
     * UTF16.lastIndexOf("abc", "a") returns 0<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", "\ud800\udc00") returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", "\ud800") returns -1<br>
     * </p>
     * <p>source is searched backwards starting at the last character.</p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param str UTF16 format Unicode string to search for
     * @return the index of the last occurrence of the codepoint in source,
     *         or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int lastIndexOf(String source, String str)
    {
        int strLength = str.length();
        // non-surrogate ends
        if (!isTrailSurrogate(str.charAt(0)) &&
            !isLeadSurrogate(str.charAt(strLength - 1))) {
            return source.lastIndexOf(str);
        }

        int result    = source.lastIndexOf(str);
        if (result >= 0) {
            // check last character
            if (isLeadSurrogate(str.charAt(strLength - 1)) &&
                (result < source.length() - 1) &&
                isTrailSurrogate(source.charAt(result + strLength + 1))) {
                return lastIndexOf(source, str, result - 1);
            }
            // check first character which is a trail surrogate
            if (isTrailSurrogate(str.charAt(0)) && result > 0 &&
                isLeadSurrogate(source.charAt(result - 1))) {
                return lastIndexOf(source, str, result - 1);
            }
        }
        return result;
    }

    /**
     * <p>Returns the index within the argument UTF16 format Unicode string of
     * the last occurrence of the argument codepoint, where the result is less
     * than or equals to fromIndex.</p>
     * <p>This method is implemented based on codepoints, hence a single
     * surrogate character will not match a supplementary character.</p>
     * <p>source is searched backwards starting at the last character starting
     * at the specified index.</p>
     * <p>
     * Examples:<br>
     * UTF16.lastIndexOf("abc", 'c', 2) returns 2<br>
     * UTF16.lastIndexOf("abc", 'c', 1) returns -1<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", 0x10000, 5) returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", 0x10000, 3) returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", 0xd800) returns -1<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param char32 codepoint to search for
     * @param fromIndex the index to start the search from. There is no
     *                  restriction on the value of fromIndex. If it is
     *                  greater than or equal to the length of this string,
     *                  it has the same effect as if it were equal to one
     *                  less than the length of this string: this entire
     *                  string may be searched. If it is negative, it has
     *                  the same effect as if it were -1: -1 is returned.
     * @return the index of the last occurrence of the codepoint in source,
     *         or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int lastIndexOf(String source, int char32, int fromIndex)
    {
        if (char32 < CODEPOINT_MIN_VALUE || char32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument char32 is not a valid codepoint");
        }
        // non-surrogate bmp
        if (char32 < LEAD_SURROGATE_MIN_VALUE ||
            (char32 > TRAIL_SURROGATE_MAX_VALUE &&
             char32 < SUPPLEMENTARY_MIN_VALUE)) {
            return source.lastIndexOf((char)char32, fromIndex);
        }
        // surrogate
        if (char32 < SUPPLEMENTARY_MIN_VALUE) {
            int result = source.lastIndexOf((char)char32, fromIndex);
            if (result >= 0) {
                if (isLeadSurrogate((char)char32) &&
                    (result < source.length() - 1) &&
                    isTrailSurrogate(source.charAt(result + 1))) {
                    return lastIndexOf(source, char32, result - 1);
                }
                // trail surrogate
                if (result > 0 &&
                    isLeadSurrogate(source.charAt(result - 1))) {
                    return lastIndexOf(source, char32, result - 1);
                }
            }
            return result;
        }
        // supplementary
        String char32str = toString(char32);
        return source.lastIndexOf(char32str, fromIndex);
    }

    /**
     * <p>Returns the index within the argument UTF16 format Unicode string of
     * the last occurrence of the argument string str, where the result is less
     * than or equals to fromIndex.</p>
     * <p>This method is implemented based on codepoints, hence a
     * "lead surrogate character + trail surrogate character" is treated as one
     * entity.
     * Hence if the str starts with trail surrogate character at index 0, a
     * source with a leading a surrogate character before str found at in
     * source will not have a valid match. Vice versa for lead surrogates
     * that ends str.
     * </p>
     * See example below.
     * <p>
     * Examples:<br>
     * UTF16.lastIndexOf("abc", "c", 2) returns 2<br>
     * UTF16.lastIndexOf("abc", "c", 1) returns -1<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", "\ud800\udc00", 5) returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", "\ud800\udc00", 3) returns 3<br>
     * UTF16.lastIndexOf("abc\ud800\udc00", "\ud800", 4) returns -1<br>
     * </p>
     * <p>source is searched backwards starting at the last character.</p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string that will be searched
     * @param str UTF16 format Unicode string to search for
     * @param fromIndex the index to start the search from. There is no
     *                  restriction on the value of fromIndex. If it is
     *                  greater than or equal to the length of this string,
     *                  it has the same effect as if it were equal to one
     *                  less than the length of this string: this entire
     *                  string may be searched. If it is negative, it has
     *                  the same effect as if it were -1: -1 is returned.
     * @return the index of the last occurrence of the codepoint in source,
     *         or -1 if the codepoint does not occur.
     * @stable ICU 2.6
     */
    public static int lastIndexOf(String source, String str, int fromIndex)
    {
        int strLength = str.length();
        // non-surrogate ends
        if (!isTrailSurrogate(str.charAt(0)) &&
            !isLeadSurrogate(str.charAt(strLength - 1))) {
            return source.lastIndexOf(str, fromIndex);
        }

        int result    = source.lastIndexOf(str, fromIndex);
        if (result >= 0) {
            // check last character
            if (isLeadSurrogate(str.charAt(strLength - 1)) &&
                (result < source.length() - 1) &&
                isTrailSurrogate(source.charAt(result + strLength))) {
                return lastIndexOf(source, str, result - 1);
            }
            // check first character which is a trail surrogate
            if (isTrailSurrogate(str.charAt(0)) && result > 0 &&
                isLeadSurrogate(source.charAt(result - 1))) {
                return lastIndexOf(source, str, result - 1);
            }
        }
        return result;
    }

    /**
     * Returns a new UTF16 format Unicode string resulting from replacing all
     * occurrences of oldChar32 in source with newChar32.
     * If the character oldChar32 does not occur in the UTF16 format Unicode
     * string source, then source will be returned. Otherwise, a new String
     * object is created that represents a codepoint sequence identical to the
     * codepoint sequence represented by source, except that every occurrence
     * of oldChar32 is replaced by an occurrence of newChar32.
     * <p>
     * Examples: <br>
     * UTF16.replace("mesquite in your cellar", 'e', 'o');<br>
     *        returns "mosquito in your collar"<br>
     * UTF16.replace("JonL", 'q', 'x');<br>
     *        returns "JonL" (no change)<br>
     * UTF16.replace("Supplementary character \ud800\udc00", 0x10000, '!');
     * <br>   returns "Supplementary character !"<br>
     * UTF16.replace("Supplementary character \ud800\udc00", 0xd800, '!');
     * <br>   returns "Supplementary character \ud800\udc00"<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string which the codepoint
     *               replacements will be based on.
     * @param oldChar32 non-zero old codepoint to be replaced.
     * @param newChar32 the new codepoint to replace oldChar32
     * @return new String derived from source by replacing every occurrence
     *         of oldChar32 with newChar32, unless when no oldChar32 is found
     *         in source then source will be returned.
     * @stable ICU 2.6
     */
    public static String replace(String source, int oldChar32,
                                 int newChar32)
    {
        if (oldChar32 <= 0 || oldChar32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument oldChar32 is not a valid codepoint");
        }
        if (newChar32 <= 0 || newChar32 > CODEPOINT_MAX_VALUE) {
            throw new IllegalArgumentException(
                                               "Argument newChar32 is not a valid codepoint");
        }

        int index     = indexOf(source, oldChar32);
        if (index == -1) {
            return source;
        }
        String       newChar32Str    = toString(newChar32);
        int          oldChar32Size   = 1;
        int          newChar32Size   = newChar32Str.length();
        StringBuffer result = new StringBuffer(source);
        int          resultIndex     = index;

        if (oldChar32 >= SUPPLEMENTARY_MIN_VALUE) {
            oldChar32Size = 2;
        }

        while (index != -1) {
            int endResultIndex  = resultIndex + oldChar32Size;
            result.replace(resultIndex, endResultIndex, newChar32Str);
            int lastEndIndex    = index + oldChar32Size;
            index       = indexOf(source, oldChar32, lastEndIndex);
            resultIndex += newChar32Size + index - lastEndIndex;
        }
        return result.toString();
    }

    /**
     * Returns a new UTF16 format Unicode string resulting from replacing all
     * occurrences of oldStr in source with newStr.
     * If the string oldStr does not occur in the UTF16 format Unicode
     * string source, then source will be returned. Otherwise, a new String
     * object is created that represents a codepoint sequence identical to the
     * codepoint sequence represented by source, except that every occurrence
     * of oldStr is replaced by an occurrence of newStr.
     * <p>
     * Examples: <br>
     * UTF16.replace("mesquite in your cellar", "e", "o");<br>
     *        returns "mosquito in your collar"<br>
     * UTF16.replace("mesquite in your cellar", "mesquite", "cat");<br>
     *        returns "cat in your cellar"<br>
     * UTF16.replace("JonL", "q", "x");<br>
     *        returns "JonL" (no change)<br>
     * UTF16.replace("Supplementary character \ud800\udc00", "\ud800\udc00",
     *               '!');
     * <br>   returns "Supplementary character !"<br>
     * UTF16.replace("Supplementary character \ud800\udc00", "\ud800", '!');
     * <br>   returns "Supplementary character \ud800\udc00"<br>
     * </p>
     * Note this method is provided as support to jdk 1.3, which does not
     * support supplementary characters to its fullest.
     * @param source UTF16 format Unicode string which the
     *               replacements will be based on.
     * @param oldStr non-zero-length string to be replaced.
     * @param newStr the new string to replace oldStr
     * @return new String derived from source by replacing every occurrence
     *         of oldStr with newStr.  When no oldStr is found
     *         in source, then source will be returned.
     * @stable ICU 2.6
     */
    public static String replace(String source, String oldStr,
                                 String newStr)
    {
        int index     = indexOf(source, oldStr);
        if (index == -1) {
            return source;
        }
        int          oldStrSize   = oldStr.length();
        int          newStrSize   = newStr.length();
        StringBuffer result       = new StringBuffer(source);
        int          resultIndex     = index;

        while (index != -1) {
            int endResultIndex  = resultIndex + oldStrSize;
            result.replace(resultIndex, endResultIndex, newStr);
            int lastEndIndex    = index + oldStrSize;
            index       = indexOf(source, oldStr, lastEndIndex);
            resultIndex += newStrSize + index - lastEndIndex;
        }
        return result.toString();
    }

    /**
     * Reverses a UTF16 format Unicode string and replaces source's content
     * with it.
     * This method will reverse surrogate characters correctly, instead of
     * blindly reversing every character.
     * <p>
     * Examples:<br>
     * UTF16.reverse(new StringBuffer(
     *             "Supplementary characters \ud800\udc00\ud801\udc01"))<br>
     * returns "\ud801\udc01\ud800\udc00 sretcarahc yratnemelppuS".
     * @param source the source StringBuffer that contains UTF16 format
     *        Unicode string to be reversed
     * @return a modified source with reversed UTF16 format Unicode string.
     * @stable ICU 2.6
     */
    public static StringBuffer reverse(StringBuffer source)
    {
    int length = source.length();
    StringBuffer result = new StringBuffer(length);
    for (int i = length; i-- > 0;) {
        char ch = source.charAt(i);
        if (isTrailSurrogate(ch) && i > 0) {
        char ch2 = source.charAt(i-1);
        if (isLeadSurrogate(ch2)) {
            result.append(ch2);
            result.append(ch);
            --i;
            continue;
        }
        }
        result.append(ch);
    }
    return result;
    }

    /**
     * Check if the string contains more Unicode code points than a certain
     * number. This is more efficient than counting all code points in the
     * entire string and comparing that number with a threshold.
     * This function may not need to scan the string at all if the length is
     * within a certain range, and never needs to count more than 'number + 1'
     * code points. Logically equivalent to (countCodePoint(s) > number). A
     * Unicode code point may occupy either one or two code units.
     * @param source The input string.
     * @param number The number of code points in the string is compared
     *               against the 'number' parameter.
     * @return boolean value for whether the string contains more Unicode code
     *         points than 'number'.
     * @stable ICU 2.4
     */
    public static boolean hasMoreCodePointsThan(String source, int number)
    {
        if (number < 0) {
            return true;
        }
        if (source == null) {
            return false;
        }
        int length = source.length();

        // length >= 0 known
        // source contains at least (length + 1) / 2 code points: <= 2
        // chars per cp
        if (((length + 1) >> 1) > number) {
            return true;
        }

        // check if source does not even contain enough chars
        int maxsupplementary = length - number;
        if (maxsupplementary <= 0) {
            return false;
        }

        // there are maxsupplementary = length - number more chars than
        // asked-for code points

        // count code points until they exceed and also check that there are
        // no more than maxsupplementary supplementary code points (char pairs)
        int start = 0;
        while (true) {
            if (length == 0) {
                return false;
            }
            if (number == 0) {
                return true;
            }
            if (isLeadSurrogate(source.charAt(start ++)) && start != length
                && isTrailSurrogate(source.charAt(start))) {
                start ++;
                if (-- maxsupplementary <= 0) {
                    // too many pairs - too few code points
                    return false;
                }
            }
            -- number;
        }
    }

    /**
     * Check if the sub-range of char array, from argument start to limit,
     * contains more Unicode code points than a certain
     * number. This is more efficient than counting all code points in the
     * entire char array range and comparing that number with a threshold.
     * This function may not need to scan the char array at all if start and
     * limit is within a certain range, and never needs to count more than
     * 'number + 1' code points.
     * Logically equivalent to (countCodePoint(source, start, limit) > number).
     * A Unicode code point may occupy either one or two code units.
     * @param source array of UTF-16 chars
     * @param start offset to substring in the source array for analyzing
     * @param limit offset to substring in the source array for analyzing
     * @param number The number of code points in the string is compared
     *               against the 'number' parameter.
     * @return boolean value for whether the string contains more Unicode code
     *         points than 'number'.
     * @exception IndexOutOfBoundsException thrown when limit &lt; start
     * @stable ICU 2.4
     */
    public static boolean hasMoreCodePointsThan(char source[], int start,
                                                int limit, int number)
    {
        int length = limit - start;
        if (length < 0 || start < 0 || limit < 0) {
            throw new IndexOutOfBoundsException(
                                                "Start and limit indexes should be non-negative and start <= limit");
        }
        if (number < 0) {
            return true;
        }
        if (source == null) {
            return false;
        }

        // length >= 0 known
        // source contains at least (length + 1) / 2 code points: <= 2
        // chars per cp
        if (((length + 1) >> 1) > number) {
            return true;
        }

        // check if source does not even contain enough chars
        int maxsupplementary = length - number;
        if (maxsupplementary <= 0) {
            return false;
        }

        // there are maxsupplementary = length - number more chars than
        // asked-for code points

        // count code points until they exceed and also check that there are
        // no more than maxsupplementary supplementary code points (char pairs)
        while (true) {
            if (length == 0) {
                return false;
            }
            if (number == 0) {
                return true;
            }
            if (isLeadSurrogate(source[start ++]) && start != limit
                && isTrailSurrogate(source[start])) {
                start ++;
                if (-- maxsupplementary <= 0) {
                    // too many pairs - too few code points
                    return false;
                }
            }
            -- number;
        }
    }

    /**
     * Check if the string buffer contains more Unicode code points than a
     * certain number. This is more efficient than counting all code points in
     * the entire string buffer and comparing that number with a threshold.
     * This function may not need to scan the string buffer at all if the
     * length is within a certain range, and never needs to count more than
     * 'number + 1' code points. Logically equivalent to
     * (countCodePoint(s) > number). A Unicode code point may occupy either one
     * or two code units.
     * @param source The input string buffer.
     * @param number The number of code points in the string buffer is compared
     *               against the 'number' parameter.
     * @return boolean value for whether the string buffer contains more
     *         Unicode code points than 'number'.
     * @stable ICU 2.4
     */
    public static boolean hasMoreCodePointsThan(StringBuffer source, int number)
    {
        if (number < 0) {
            return true;
        }
        if (source == null) {
            return false;
        }
        int length = source.length();

        // length >= 0 known
        // source contains at least (length + 1) / 2 code points: <= 2
        // chars per cp
        if (((length + 1) >> 1) > number) {
            return true;
        }

        // check if source does not even contain enough chars
        int maxsupplementary = length - number;
        if (maxsupplementary <= 0) {
            return false;
        }

        // there are maxsupplementary = length - number more chars than
        // asked-for code points

        // count code points until they exceed and also check that there are
        // no more than maxsupplementary supplementary code points (char pairs)
        int start = 0;
        while (true) {
            if (length == 0) {
                return false;
            }
            if (number == 0) {
                return true;
            }
            if (isLeadSurrogate(source.charAt(start ++)) && start != length
                && isTrailSurrogate(source.charAt(start))) {
                start ++;
                if (-- maxsupplementary <= 0) {
                    // too many pairs - too few code points
                    return false;
                }
            }
            -- number;
        }
    }

    /**
     * Cover JDK 1.5 API.  Create a String from an array of codePoints.
     * @param codePoints the code array
     * @param offset     the start of the text in the code point array
     * @param count      the number of code points
     * @return a String representing the code points between offset and count
     * @throws IllegalArgumentException if an invalid code point is encountered
     * @throws IndexOutOfBoundsException  if the offset or count are out of bounds.
     * @draft ICU 3.0
     * @provisional This API might change or be removed in a future release.
     */
    public static String newString(int[] codePoints, int offset, int count) {
        if (count < 0) {
            throw new IllegalArgumentException();
        }
        char[] chars = new char[count];
        int w = 0;
        for (int r = offset, e = offset + count; r < e; ++r) {
            int cp = codePoints[r];
            if (cp < 0 || cp > 0x10ffff) {
                throw new IllegalArgumentException();
            }
            while (true) {
                try {
                    if (cp < 0x010000) {
                        chars[w] = (char)cp;
                        w++;
                    } else {
                        chars[w] = (char)(LEAD_SURROGATE_OFFSET_ +
                                          (cp >> LEAD_SURROGATE_SHIFT_));
                        chars[w+1] = (char)(TRAIL_SURROGATE_MIN_VALUE +
                                            (cp & TRAIL_SURROGATE_MASK_));
                        w += 2;
                    }
                    break;
                }
                catch (IndexOutOfBoundsException ex) {
                    int newlen = (int)(Math.ceil((double)codePoints.length * (w+2) / (r-offset+1)));
                    char[] temp = new char[newlen];
                    System.arraycopy(chars, 0, temp, 0, w);
                    chars = temp;
                }
            }
        }
        return new String(chars, 0, w);
    }

    /**
     * <p>UTF16 string comparator class.
     * Allows UTF16 string comparison to be done with the various modes</p>
     * <ul>
     * <li> Code point comparison or code unit comparison
     * <li> Case sensitive comparison, case insensitive comparison or case
     *      insensitive comparison with special handling for character 'i'.
     * </ul>
     * <p>The code unit or code point comparison differ only when comparing
     * supplementary code points (&#92;u10000..&#92;u10ffff) to BMP code points
     * near the end of the BMP (i.e., &#92;ue000..&#92;uffff). In code unit
     * comparison, high BMP code points sort after supplementary code points
     * because they are stored as pairs of surrogates which are at
     * &#92;ud800..&#92;udfff.</p>
     * @see #FOLD_CASE_DEFAULT
     * @see #FOLD_CASE_EXCLUDE_SPECIAL_I
     * @stable ICU 2.1
     */
    public static final class StringComparator implements java.util.Comparator
    {
        // public constructor ------------------------------------------------

        /**
         * Default constructor that does code unit comparison and case
         * sensitive comparison.
         * @stable ICU 2.1
         */
        public StringComparator()
        {
            this(false, false, FOLD_CASE_DEFAULT);
        }

        /**
         * Constructor that does comparison based on the argument options.
         * @param codepointcompare flag to indicate true for code point
         *        comparison or false for code unit comparison.
         * @param ignorecase false for case sensitive comparison, true for
         *        case-insensitive comparison
         * @param foldcaseoption FOLD_CASE_DEFAULT or
         *        FOLD_CASE_EXCLUDE_SPECIAL_I. This option is used only when
         *        ignorecase is set to true. If ignorecase is false, this option
         *        is ignored.
         * @see #FOLD_CASE_DEFAULT
         * @see #FOLD_CASE_EXCLUDE_SPECIAL_I
         * @throws IllegalArgumentException if foldcaseoption is out of range
         * @stable ICU 2.4
         */
        public StringComparator(boolean codepointcompare,
                                boolean ignorecase,
                                int foldcaseoption)
        {
            setCodePointCompare(codepointcompare);
            m_ignoreCase_ = ignorecase;
            if (foldcaseoption < FOLD_CASE_DEFAULT
                || foldcaseoption > FOLD_CASE_EXCLUDE_SPECIAL_I) {
                throw new IllegalArgumentException("Invalid fold case option");
            }
            m_foldCase_ = foldcaseoption;
        }

        // public data member ------------------------------------------------

        /**
         * <p>Option value for case folding comparison:</p>
         * <p>Comparison is case insensitive, strings are folded using default
         * mappings defined in Unicode data file CaseFolding.txt, before
         * comparison.
         * </p>
         * @stable ICU 2.4
         */
        public static final int FOLD_CASE_DEFAULT = 0;
        /**
         * <p>Option value for case folding comparison:</p>
         * <p>Comparison is case insensitive, strings are folded using modified
         * mappings defined in Unicode data file CaseFolding.txt, before
         * comparison.
         * </p>
         * <p>The modified set of mappings is provided in a Unicode data file
         * CaseFolding.txt to handle dotted I and dotless i appropriately for
         * Turkic languages (tr, az).</p>
         * <p>Before Unicode 3.2, CaseFolding.txt contains mappings marked with
         * 'I' that are to be included for default mappings and excluded for
         * the Turkic-specific mappings.</p>
         * <p>Unicode 3.2 CaseFolding.txt instead contains mappings marked with
         * 'T' that are to be excluded for default mappings and included for
         * the Turkic-specific mappings.</p>
         * @stable ICU 2.4
         */
        public static final int FOLD_CASE_EXCLUDE_SPECIAL_I = 1;

        // public methods ----------------------------------------------------

        // public setters ----------------------------------------------------

        /**
         * Sets the comparison mode to code point compare if flag is true.
         * Otherwise comparison mode is set to code unit compare
         * @param flag true for code point compare, false for code unit compare
         * @stable ICU 2.4
         */
        public void setCodePointCompare(boolean flag)
        {
            if (flag) {
                m_codePointCompare_ = Normalizer.COMPARE_CODE_POINT_ORDER;
            }
            else {
                m_codePointCompare_ = 0;
            }
        }

        /**
         * Sets the Comparator to case-insensitive comparison mode if argument
         * is true, otherwise case sensitive comparison mode if set to false.
         * @param ignorecase true for case-insitive comparison, false for
         *        case sensitive comparison
         * @param foldcaseoption FOLD_CASE_DEFAULT or
         *        FOLD_CASE_EXCLUDE_SPECIAL_I. This option is used only when
         *        ignorecase is set to true. If ignorecase is false, this option
         *        is ignored.
         * @see #FOLD_CASE_DEFAULT
         * @see #FOLD_CASE_EXCLUDE_SPECIAL_I
         * @stable ICU 2.4
         */
        public void setIgnoreCase(boolean ignorecase, int foldcaseoption)
        {
            m_ignoreCase_ = ignorecase;
            if (foldcaseoption < FOLD_CASE_DEFAULT
                || foldcaseoption > FOLD_CASE_EXCLUDE_SPECIAL_I) {
                throw new IllegalArgumentException("Invalid fold case option");
            }
            m_foldCase_ = foldcaseoption;
        }

        // public getters ----------------------------------------------------

        /**
         * Checks if the comparison mode is code point compare.
         * @return true for code point compare, false for code unit compare
         * @stable ICU 2.4
         */
        public boolean getCodePointCompare()
        {
            return m_codePointCompare_ == Normalizer.COMPARE_CODE_POINT_ORDER;
        }

        /**
         * Checks if Comparator is in the case insensitive mode.
         * @return true if Comparator performs case insensitive comparison,
         *         false otherwise
         * @stable ICU 2.4
         */
        public boolean getIgnoreCase()
        {
            return m_ignoreCase_;
        }

        /**
         * Gets the fold case options set in Comparator to be used with case
         * insensitive comparison.
         * @return either FOLD_CASE_DEFAULT or FOLD_CASE_EXCLUDE_SPECIAL_I
         * @see #FOLD_CASE_DEFAULT
         * @see #FOLD_CASE_EXCLUDE_SPECIAL_I
         * @stable ICU 2.4
         */
        public int getIgnoreCaseOption()
        {
            return m_foldCase_;
        }

        // public other methods ----------------------------------------------

        /**
         * Compare two strings depending on the options selected during
         * construction.
         * @param a first source string.
         * @param b second source string.
         * @return 0 returned if a == b. If a < b, a negative value is returned.
         *         Otherwise if a > b, a positive value is returned.
         * @exception ClassCastException thrown when either a or b is not a
         *            String object
         * @stable ICU 2.4
         */
        public int compare(Object a, Object b)
        {
            String str1 = (String)a;
            String str2 = (String)b;

            if (str1 == str2) {
                return 0;
            }
            if (str1 == null) {
                return -1;
            }
            if (str2 == null) {
                return 1;
            }

            if (m_ignoreCase_) {
                return compareCaseInsensitive(str1, str2);
            }
            return compareCaseSensitive(str1, str2);
        }

        // private data member ----------------------------------------------

        /**
         * Code unit comparison flag. True if code unit comparison is required.
         * False if code point comparison is required.
         */
        private int m_codePointCompare_;

        /**
         * Fold case comparison option.
         */
        private int m_foldCase_;

        /**
         * Flag indicator if ignore case is to be used during comparison
         */
        private boolean m_ignoreCase_;

        /**
         * Code point order offset for surrogate characters
         */
        private static final int CODE_POINT_COMPARE_SURROGATE_OFFSET_ = 0x2800;

        // private method ---------------------------------------------------

        /**
         * Compares case insensitive. This is a direct port of ICU4C, to make
         * maintainence life easier.
         * @param s1 first string to compare
         * @param s2 second string to compare
         * @return -1 is s1 &lt; s2, 0 if equals,
         */
        private int compareCaseInsensitive(String s1, String s2)
        {
            return NormalizerImpl.cmpEquivFold(s1, s2,
                                               m_foldCase_ | m_codePointCompare_
                                               | Normalizer.COMPARE_IGNORE_CASE);
        }

        /**
         * Compares case sensitive. This is a direct port of ICU4C, to make
         * maintainence life easier.
         * @param s1 first string to compare
         * @param s2 second string to compare
         * @return -1 is s1 &lt; s2, 0 if equals,
         */
        private int compareCaseSensitive(String s1, String s2)
        {
            // compare identical prefixes - they do not need to be fixed up
            // limit1 = start1 + min(lenght1, length2)
            int length1 = s1.length();
            int length2 = s2.length();
            int minlength = length1;
            int result = 0;
            if (length1 < length2) {
                result = -1;
            }
            else if (length1 > length2) {
                result = 1;
                minlength = length2;
            }

            char c1 = 0;
            char c2 = 0;
            int index = 0;
            for (; index < minlength; index ++) {
                c1 = s1.charAt(index);
                c2 = s2.charAt(index);
                // check pseudo-limit
                if (c1 != c2) {
                    break;
                }
            }

            if (index == minlength) {
                return result;
            }

            boolean codepointcompare
                = m_codePointCompare_ == Normalizer.COMPARE_CODE_POINT_ORDER;
            // if both values are in or above the surrogate range, fix them up
            if (c1 >= LEAD_SURROGATE_MIN_VALUE
                && c2 >= LEAD_SURROGATE_MIN_VALUE && codepointcompare) {
                // subtract 0x2800 from BMP code points to make them smaller
                // than supplementary ones
                if ((c1 <= LEAD_SURROGATE_MAX_VALUE && (index + 1) != length1
                     && isTrailSurrogate(s1.charAt(index + 1)))
                    || (isTrailSurrogate(c1) && index != 0
                        && isLeadSurrogate(s1.charAt(index - 1)))) {
                    // part of a surrogate pair, leave >=d800
                }
                else {
                    // BMP code point - may be surrogate code point - make
                    // < d800
                    c1 -= CODE_POINT_COMPARE_SURROGATE_OFFSET_;
                }

                if ((c2 <= LEAD_SURROGATE_MAX_VALUE
                     && (index + 1) != length2
                     && isTrailSurrogate(s2.charAt(index + 1))) ||
                    (isTrailSurrogate(c2) && index != 0
                     && isLeadSurrogate(s2.charAt(index - 1)))) {
                    // part of a surrogate pair, leave >=d800
                }
                else {
                    // BMP code point - may be surrogate code point - make <d800
                    c2 -= CODE_POINT_COMPARE_SURROGATE_OFFSET_;
                }
            }

            // now c1 and c2 are in UTF-32-compatible order
            return c1 - c2;
        }
    }

    // private data members -------------------------------------------------

    /**
     * Shift value for lead surrogate to form a supplementary character.
     */
    private static final int LEAD_SURROGATE_SHIFT_ = 10;

    /**
     * Mask to retrieve the significant value from a trail surrogate.
     */
    private static final int TRAIL_SURROGATE_MASK_     = 0x3FF;

    /**
     * Value that all lead surrogate starts with
     */
    private static final int LEAD_SURROGATE_OFFSET_ =
        LEAD_SURROGATE_MIN_VALUE -
        (SUPPLEMENTARY_MIN_VALUE
         >> LEAD_SURROGATE_SHIFT_);

    // private methods ------------------------------------------------------

    /**
     * <p>Converts argument code point and returns a String object representing
     * the code point's value in UTF16 format.</p>
     * <p>This method does not check for the validity of the codepoint, the
     * results are not guaranteed if a invalid codepoint is passed as
     * argument.</p>
     * <p>The result is a string whose length is 1 for non-supplementary code
     * points, 2 otherwise.</p>
     * @param ch code point
     * @return string representation of the code point
     */
    private static String toString(int ch)
    {
        if (ch < SUPPLEMENTARY_MIN_VALUE) {
            return String.valueOf((char)ch);
        }

        StringBuffer result = new StringBuffer();
        result.append(getLeadSurrogate(ch));
        result.append(getTrailSurrogate(ch));
        return result.toString();
    }
}