glibc/sysdeps/generic/dl-hash.h

/* Compute hash value for given string according to ELF standard.
   Copyright (C) 1995,1996,1997,1998,2003,2005 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C 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 2.1 of the License, or (at your option) any later version.

   The GNU C 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 the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#ifndef _DL_HASH_H
#define _DL_HASH_H	1


/* This is the hashing function specified by the ELF ABI.  In the
   first five operations no overflow is possible so we optimized it a
   bit.  */
static unsigned int
_dl_elf_hash (const char *name_arg)
{
  const unsigned char *name = (const unsigned char *) name_arg;
  unsigned long int hash = 0;
  if (*name != '\0')
    {
      hash = *name++;
      if (*name != '\0')
	{
	  hash = (hash << 4) + *name++;
	  if (*name != '\0')
	    {
	      hash = (hash << 4) + *name++;
	      if (*name != '\0')
		{
		  hash = (hash << 4) + *name++;
		  if (*name != '\0')
		    {
		      hash = (hash << 4) + *name++;
		      while (*name != '\0')
			{
			  unsigned long int hi;
			  hash = (hash << 4) + *name++;
			  hi = hash & 0xf0000000;

			  /* The algorithm specified in the ELF ABI is as
			     follows:

			     if (hi != 0)
			       hash ^= hi >> 24;

			     hash &= ~hi;

			     But the following is equivalent and a lot
			     faster, especially on modern processors.  */

			  hash ^= hi;
			  hash ^= hi >> 24;
			}
		    }
		}
	    }
	}
    }
  return hash;
}

#endif /* dl-hash.h */