/* GNU Mailutils -- a suite of utilities for electronic mail
   Copyright (C) 1999-2025 Free Software Foundation, Inc.

   This 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 3 of the License, or (at your option) any later version.

   This 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 this library.  If not, see 
   <http://www.gnu.org/licenses/>. */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <unistd.h>
#include <mailutils/cctype.h>

/* Based on strstr from GNU libc (Stephen R. van den Berg,
   berg@pool.informatik.rwth-aachen.de) */
char *
mu_c_strcasestr (const char *a_haystack, const char *a_needle)
{
  register const unsigned char *haystack = (unsigned char*) a_haystack,
    *needle = (unsigned char*) a_needle;
  register unsigned int b, c;

#define U(c) mu_toupper (c)
  if ((b = U (*needle)))
    {
      haystack--;		
      do
	{
	  if (!(c = *++haystack))
	    goto ret0;
	}
      while (U (c) != b);

      if (!(c = *++needle))
	goto foundneedle;

      c = U (c);
      ++needle;
      goto jin;

      for (;;)
        { 
          register unsigned int a;
	  register const unsigned char *rhaystack, *rneedle;

	  do
	    {
	      if (!(a = *++haystack))
		goto ret0;
	      if (U (a) == b)
		break;
	      if (!(a = *++haystack))
		goto ret0;
shloop:       ;
            }
          while (U (a) != b);
	  
jin:     if (!(a = *++haystack))
	    goto ret0;

	  if (U (a) != c)
	    goto shloop;

	  if (U (*(rhaystack = haystack-- + 1)) ==
	      (a = U (*(rneedle = needle))))
	    do
	      {
		if (!a)
		  goto foundneedle;
		if (U (*++rhaystack) != (a = U (*++needle)))
		  break;
		if (!a)
		  goto foundneedle;
	      }
	    while (U (*++rhaystack) == (a = U (*++needle)));

	  needle = rneedle;

	  if (!a)
	    break;
        }
    }
foundneedle:
  return (char*)haystack;
ret0:
  return NULL;

#undef U
}  
