/*
 * Copyright (C) 1999-2024 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 2.1
 * 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-32
 */

/* Specification: Unicode 3.1 Standard Annex #19 */

/* Here we accept FFFE0000/0000FEFF marks as endianness indicators
   everywhere in the stream, not just at the beginning. (This is contrary
   to what #19 D36c specifies, but it allows concatenation of byte
   sequences to work flawlessly, while disagreeing with #19 behaviour
   only for strings containing U+FEFF characters, which is quite rare.)
   The default is big-endian. */
/* The state is 0 if big-endian, 1 if little-endian. */
static int
utf32_mbtowc (conv_t conv, ucs4_t *pwc, const unsigned char *s, size_t n)
{
  state_t state = conv->ibyteorder;
  int count = 0;
  for (; n >= 4 && count <= RET_COUNT_MAX && count <= INT_MAX-4;) {
    ucs4_t wc = (state
                  ?    (ucs4_t) s[0]
                    + ((ucs4_t) s[1] << 8)
                    + ((ucs4_t) s[2] << 16)
                    + ((ucs4_t) s[3] << 24)
                  :   ((ucs4_t) s[0] << 24)
                    + ((ucs4_t) s[1] << 16)
                    + ((ucs4_t) s[2] << 8)
                    +  (ucs4_t) s[3]);
    if (wc == 0x0000feff) {
    } else if (wc == 0xfffe0000u) {
      state ^= 1;
    } else {
      if (wc < 0x110000 && !(wc >= 0xd800 && wc < 0xe000)) {
        *pwc = wc;
        conv->ibyteorder = state;
        return count+4;
      } else {
        conv->ibyteorder = state;
        return RET_SHIFT_ILSEQ(count);
      }
    }
    s += 4; n -= 4; count += 4;
  }
  conv->ibyteorder = state;
  return RET_TOOFEW(count);
}

/* We output UTF-32 in big-endian order, with byte-order mark. */
/* The state is 0 at the beginning, 1 after the BOM has been written. */
static int
utf32_wctomb (conv_t conv, unsigned char *r, ucs4_t wc, size_t n)
{
  if (wc < 0x110000 && !(wc >= 0xd800 && wc < 0xe000)) {
    int count = 0;
    if (!conv->ostate) {
      if (n >= 4) {
        r[0] = 0x00;
        r[1] = 0x00;
        r[2] = 0xFE;
        r[3] = 0xFF;
        r += 4; n -= 4; count += 4;
      } else
        return RET_TOOSMALL;
    }
    if (wc < 0x110000) {
      if (n >= 4) {
        r[0] = 0;
        r[1] = (unsigned char) (wc >> 16);
        r[2] = (unsigned char) (wc >> 8);
        r[3] = (unsigned char) wc;
        conv->ostate = 1;
        return count+4;
      } else
        return RET_TOOSMALL;
    }
  }
  return RET_ILUNI;
}