/*
 * Copyright (C) 1999-2001, 2004, 2016 Free Software Foundation, Inc.
 * This file is part of the GNU LIBICONV Library.
 *
 * The GNU LIBICONV Library is free software; you can redistribute it
 * and/or modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * The GNU LIBICONV Library is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with the GNU LIBICONV Library; see the file COPYING.LIB.
 * If not, see <https://www.gnu.org/licenses/>.
 */

/*
 * UTF-8
 */

/* Specification: RFC 3629 */

static int
utf8_mbtowc (conv_t conv, ucs4_t *pwc, const unsigned char *s, size_t n)
{
  unsigned char c = s[0];

  if (c < 0x80) {
    *pwc = c;
    return 1;
  } else if (c < 0xc2) {
    return RET_ILSEQ;
  } else if (c < 0xe0) {
    if (n < 2)
      return RET_TOOFEW(0);
    if (!((s[1] ^ 0x80) < 0x40))
      return RET_ILSEQ;
    *pwc = ((ucs4_t) (c & 0x1f) << 6)
           | (ucs4_t) (s[1] ^ 0x80);
    return 2;
  } else if (c < 0xf0) {
    if (n < 3)
      return RET_TOOFEW(0);
    if (!((s[1] ^ 0x80) < 0x40 && (s[2] ^ 0x80) < 0x40
          && (c >= 0xe1 || s[1] >= 0xa0)
          && (c != 0xed || s[1] < 0xa0)))
      return RET_ILSEQ;
    *pwc = ((ucs4_t) (c & 0x0f) << 12)
           | ((ucs4_t) (s[1] ^ 0x80) << 6)
           | (ucs4_t) (s[2] ^ 0x80);
    return 3;
  } else if (c < 0xf8 && sizeof(ucs4_t)*8 >= 32) {
    if (n < 4)
      return RET_TOOFEW(0);
    if (!((s[1] ^ 0x80) < 0x40 && (s[2] ^ 0x80) < 0x40
          && (s[3] ^ 0x80) < 0x40
          && (c >= 0xf1 || s[1] >= 0x90)
          && (c < 0xf4 || (c == 0xf4 && s[1] < 0x90))))
      return RET_ILSEQ;
    *pwc = ((ucs4_t) (c & 0x07) << 18)
           | ((ucs4_t) (s[1] ^ 0x80) << 12)
           | ((ucs4_t) (s[2] ^ 0x80) << 6)
           | (ucs4_t) (s[3] ^ 0x80);
    return 4;
  } else
    return RET_ILSEQ;
}

static int
utf8_wctomb (conv_t conv, unsigned char *r, ucs4_t wc, size_t n) /* n == 0 is acceptable */
{
  int count;
  if (wc < 0x80)
    count = 1;
  else if (wc < 0x800)
    count = 2;
  else if (wc < 0x10000) {
    if (wc < 0xd800 || wc >= 0xe000)
      count = 3;
    else
      return RET_ILUNI;
  } else if (wc < 0x110000)
    count = 4;
  else
    return RET_ILUNI;
  if (n < count)
    return RET_TOOSMALL;
  switch (count) { /* note: code falls through cases! */
    case 4: r[3] = 0x80 | (wc & 0x3f); wc = wc >> 6; wc |= 0x10000;
    case 3: r[2] = 0x80 | (wc & 0x3f); wc = wc >> 6; wc |= 0x800;
    case 2: r[1] = 0x80 | (wc & 0x3f); wc = wc >> 6; wc |= 0xc0;
    case 1: r[0] = wc;
  }
  return count;
}