/* Compare UTF-16 strings.
   Copyright (C) 1999, 2002, 2006, 2009-2017 Free Software Foundation, Inc.
   Written by Bruno Haible <bruno@clisp.org>, 2002.

   This program is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.
   This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include "unistr.h"

int
u16_strcmp (const uint16_t *s1, const uint16_t *s2)
{
  /* Note that the UTF-16 encoding does NOT preserve lexicographic order.
     Namely, if uc1 is a 16-bit character and [uc2a,uc2b] is a surrogate pair,
     we must enforce uc1 < [uc2a,uc2b], even if uc1 > uc2a.  */
  for (;;)
    {
      uint16_t c1 = *s1++;
      uint16_t c2 = *s2++;
      if (c1 != 0 && c1 == c2)
        continue;
      if (c1 < 0xd800 || c1 >= 0xe000)
        {
          if (!(c2 < 0xd800 || c2 >= 0xe000))
            /* c2 is a surrogate, but c1 is not.  */
            return -1;
        }
      else
        {
          if (c2 < 0xd800 || c2 >= 0xe000)
            /* c1 is a surrogate, but c2 is not.  */
            return 1;
        }
      return (int)c1 - (int)c2;
      /* > 0 if c1 > c2, < 0 if c1 < c2. */
    }
}