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/*
 * 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/>.
 */

/*
 * UCS-4
 */

/* Here we accept FFFE0000/0000FEFF marks as endianness indicators everywhere
   in the stream, not just at the beginning. The default is big-endian. */
/* The state is 0 if big-endian, 1 if little-endian. */
static int
ucs4_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 <= 0x7fffffff) {
      *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);
}

/* But we output UCS-4 in big-endian order, without byte-order mark. */
static int
ucs4_wctomb (conv_t conv, unsigned char *r, ucs4_t wc, size_t n)
{
  if (wc <= 0x7fffffff) {
    if (n >= 4) {
      r[0] = (unsigned char) (wc >> 24);
      r[1] = (unsigned char) (wc >> 16);
      r[2] = (unsigned char) (wc >> 8);
      r[3] = (unsigned char) wc;
      return 4;
    } else
      return RET_TOOSMALL;
  } else
    return RET_ILUNI;
}
thodg/libiconv/lib/ucs4.h

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lib/ucs4.h
