gnulib/lib/unistr/u16-cmp.c

/* Compare pieces of UTF-16 strings.
   Copyright (C) 1999, 2002, 2006, 2009-2020 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 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.

   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_cmp (const uint16_t *s1, const uint16_t *s2, size_t n)
{
  /* 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 (; n > 0;)
    {
      uint16_t c1 = *s1++;
      uint16_t c2 = *s2++;
      if (c1 == c2)
        {
          n--;
          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. */
    }
  return 0;
}