sysdeps/generic/dl-hash.h

   1 /* Compute hash value for given string according to ELF standard.
   2    Copyright (C) 1995, 1996, 1997, 1998, 2003 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #ifndef _DL_HASH_H
  21 #define _DL_HASH_H      1
  22
  23
  24 /* This is the hashing function specified by the ELF ABI.  In the
  25    first five operations no overflow is possible so we optimized it a
  26    bit.  */
  27 static unsigned int
  28 _dl_elf_hash (const unsigned char *name)
  29 {
  30   unsigned long int hash = 0;
  31   if (*name != '\0')
  32     {
  33       hash = *name++;
  34       if (*name != '\0')
  35         {
  36           hash = (hash << 4) + *name++;
  37           if (*name != '\0')
  38             {
  39               hash = (hash << 4) + *name++;
  40               if (*name != '\0')
  41                 {
  42                   hash = (hash << 4) + *name++;
  43                   if (*name != '\0')
  44                     {
  45                       hash = (hash << 4) + *name++;
  46                       while (*name != '\0')
  47                         {
  48                           unsigned long int hi;
  49                           hash = (hash << 4) + *name++;
  50                           hi = hash & 0xf0000000;
  51
  52                           /* The algorithm specified in the ELF ABI is as
  53                              follows:
  54
  55                              if (hi != 0)
  56                                hash ^= hi >> 24;
  57
  58                              hash &= ~hi;
  59
  60                              But the following is equivalent and a lot
  61                              faster, especially on modern processors.  */
  62
  63                           hash ^= hi;
  64                           hash ^= hi >> 24;
  65                         }
  66                     }
  67                 }
  68             }
  69         }
  70     }
  71   return hash;
  72 }
  73
  74 #endif /* dl-hash.h */