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glibc  2.9
hash-string.c
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00001 /* Implements a string hashing function.
00002    Copyright (C) 1995, 1997, 1998, 2000, 2003 Free Software Foundation, Inc.
00003    This file is part of the GNU C Library.
00004 
00005    The GNU C Library is free software; you can redistribute it and/or
00006    modify it under the terms of the GNU Lesser General Public
00007    License as published by the Free Software Foundation; either
00008    version 2.1 of the License, or (at your option) any later version.
00009 
00010    The GNU C Library is distributed in the hope that it will be useful,
00011    but WITHOUT ANY WARRANTY; without even the implied warranty of
00012    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00013    Lesser General Public License for more details.
00014 
00015    You should have received a copy of the GNU Lesser General Public
00016    License along with the GNU C Library; if not, write to the Free
00017    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
00018    02111-1307 USA.  */
00019 
00020 #include "hash-string.h"
00021 
00022 
00023 /* Defines the so called `hashpjw' function by P.J. Weinberger
00024    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
00025    1986, 1987 Bell Telephone Laboratories, Inc.]  */
00026 unsigned long int
00027 __hash_string (str_param)
00028      const char *str_param;
00029 {
00030   unsigned long int hval, g;
00031   const char *str = str_param;
00032 
00033   /* Compute the hash value for the given string.  */
00034   hval = 0;
00035   while (*str != '\0')
00036     {
00037       hval <<= 4;
00038       hval += (unsigned char) *str++;
00039       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
00040       if (g != 0)
00041        {
00042          hval ^= g >> (HASHWORDBITS - 8);
00043          hval ^= g;
00044        }
00045     }
00046   return hval;
00047 }