/* Convert UTF-16 string to UTF-8 string.

   Copyright (C) 2002, 2006-2007, 2009-2025 Free Software Foundation, Inc.

   Written by Bruno Haible <bruno@clisp.org>, 2002.

   This file is free software.

   It is dual-licensed under "the GNU LGPLv3+ or the GNU GPLv2+".

   You can redistribute it and/or modify it under either

     - the terms of the GNU Lesser General Public License as published

       by the Free Software Foundation, either version 3, or (at your

       option) any later version, or

     - the terms of the GNU General Public License as published by the

       Free Software Foundation; either version 2, or (at your option)

       any later version, or

     - the same dual license "the GNU LGPLv3+ or the GNU GPLv2+".

   This file 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 and the GNU General Public License

   for more details.

   You should have received a copy of the GNU Lesser General Public

   License and of the GNU General Public License along with this

   program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include "unistr.h"

#define FUNC u16_to_u8

#define SRC_UNIT uint16_t

#define DST_UNIT uint8_t

#include <errno.h>

#include <stdlib.h>

#include <string.h>

DST_UNIT *

FUNC (const SRC_UNIT *s, size_t n, DST_UNIT *resultbuf, size_t *lengthp)

{

  const SRC_UNIT *s_end = s + n;

  /* Output string accumulator.  */

  DST_UNIT *result;

  size_t allocated;

  size_t length;

  if (resultbuf != NULL)

    {

      result = resultbuf;

      allocated = *lengthp;

    }

  else

    {

      result = NULL;

      allocated = 0;

    }

  length = 0;

  /* Invariants:

     result is either == resultbuf or == NULL or malloc-allocated.

     If length > 0, then result != NULL.  */

  while (s < s_end)

    {

      ucs4_t uc;

      int count;

      /* Fetch a Unicode character from the input string.  */

      count = u16_mbtoucr (&uc, s, s_end - s);

      if (count < 0)

        {

          if (!(result == resultbuf || result == NULL))

            free (result);

          errno = EILSEQ;

          return NULL;

        }

      s += count;

      /* Store it in the output string.  */

      count = u8_uctomb (result + length, uc, allocated - length);

      if (count == -1)

        {

          if (!(result == resultbuf || result == NULL))

            free (result);

          errno = EILSEQ;

          return NULL;

        }

      if (count == -2)

        {

          DST_UNIT *memory;

          allocated = (allocated > 0 ? 2 * allocated : 12);

          if (length + 6 > allocated)

            allocated = length + 6;

          if (result == resultbuf || result == NULL)

            memory = (DST_UNIT *) malloc (allocated * sizeof (DST_UNIT));

          else

            memory =

              (DST_UNIT *) realloc (result, allocated * sizeof (DST_UNIT));

          if (memory == NULL)

            {

              if (!(result == resultbuf || result == NULL))

                free (result);

              errno = ENOMEM;

              return NULL;

            }

          if (result == resultbuf && length > 0)

            memcpy ((char *) memory, (char *) result,

                    length * sizeof (DST_UNIT));

          result = memory;

          count = u8_uctomb (result + length, uc, allocated - length);

          if (count < 0)

            abort ();

        }

      length += count;

    }

  if (length == 0)

    {

      if (result == NULL)

        {

          /* Return a non-NULL value.  NULL means error.  */

          result = (DST_UNIT *) malloc (1);

          if (result == NULL)

            {

              errno = ENOMEM;

              return NULL;

            }

        }

    }

  else if (result != resultbuf && length < allocated)

    {

      /* Shrink the allocated memory if possible.  */

      DST_UNIT *memory;

      memory = (DST_UNIT *) realloc (result, length * sizeof (DST_UNIT));

      if (memory != NULL)

        result = memory;

    }

  *lengthp = length;

  return result;

}