/* Look at first character in UTF-8 string.
   Copyright (C) 1999-2000, 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"

int
u8_strmblen (const uint8_t *s)
{
  /* Keep in sync with unistr.h and u8-mbtouc-aux.c.  */
  uint8_t c = *s;

  if (c < 0x80)
    return (c != 0 ? 1 : 0);
  if (c >= 0xc2)
    {
      if (c < 0xe0)
        {
          if ((s[1] ^ 0x80) < 0x40)
            return 2;
        }
      else if (c < 0xf0)
        {
          if ((s[1] ^ 0x80) < 0x40 && (s[2] ^ 0x80) < 0x40
              && (c >= 0xe1 || s[1] >= 0xa0)
              && (c != 0xed || s[1] < 0xa0))
            return 3;
        }
      else if (c <= 0xf4)
        {
          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 4;
        }
    }
  /* invalid or incomplete multibyte character */
  return -1;
}
