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       1                 :            : /* Compute hash value for given string according to ELF standard.
       2                 :            :    Copyright (C) 2006 Red Hat, Inc.
       3                 :            :    This file is part of elfutils.
       4                 :            :    Written by Ulrich Drepper <drepper@redhat.com>, 1995.
       5                 :            : 
       6                 :            :    This file is free software; you can redistribute it and/or modify
       7                 :            :    it under the terms of either
       8                 :            : 
       9                 :            :      * the GNU Lesser General Public License as published by the Free
      10                 :            :        Software Foundation; either version 3 of the License, or (at
      11                 :            :        your option) any later version
      12                 :            : 
      13                 :            :    or
      14                 :            : 
      15                 :            :      * the GNU General Public License as published by the Free
      16                 :            :        Software Foundation; either version 2 of the License, or (at
      17                 :            :        your option) any later version
      18                 :            : 
      19                 :            :    or both in parallel, as here.
      20                 :            : 
      21                 :            :    elfutils is distributed in the hope that it will be useful, but
      22                 :            :    WITHOUT ANY WARRANTY; without even the implied warranty of
      23                 :            :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      24                 :            :    General Public License for more details.
      25                 :            : 
      26                 :            :    You should have received copies of the GNU General Public License and
      27                 :            :    the GNU Lesser General Public License along with this program.  If
      28                 :            :    not, see <http://www.gnu.org/licenses/>.  */
      29                 :            : 
      30                 :            : #ifndef _DL_HASH_H
      31                 :            : #define _DL_HASH_H      1
      32                 :            : 
      33                 :            : 
      34                 :            : /* This is the hashing function specified by the ELF ABI.  In the
      35                 :            :    first five operations no overflow is possible so we optimized it a
      36                 :            :    bit.  */
      37                 :            : static inline unsigned int
      38                 :            : __attribute__ ((__pure__))
      39                 :      88832 : _dl_elf_hash (const char *name)
      40                 :            : {
      41                 :      88832 :   const unsigned char *iname = (const unsigned char *) name;
      42                 :      88832 :   unsigned int hash = (unsigned int) *iname++;
      43         [ +  + ]:      88832 :   if (*iname != '\0')
      44                 :            :     {
      45                 :      88810 :       hash = (hash << 4) + (unsigned int) *iname++;
      46         [ +  + ]:      88810 :       if (*iname != '\0')
      47                 :            :         {
      48                 :      88629 :           hash = (hash << 4) + (unsigned int) *iname++;
      49         [ +  + ]:      88629 :           if (*iname != '\0')
      50                 :            :             {
      51                 :      86816 :               hash = (hash << 4) + (unsigned int) *iname++;
      52         [ +  + ]:      86816 :               if (*iname != '\0')
      53                 :            :                 {
      54                 :      68806 :                   hash = (hash << 4) + (unsigned int) *iname++;
      55         [ +  + ]:      78190 :                   while (*iname != '\0')
      56                 :            :                     {
      57                 :            :                       unsigned int hi;
      58                 :       9384 :                       hash = (hash << 4) + (unsigned int) *iname++;
      59                 :       9384 :                       hi = hash & 0xf0000000;
      60                 :            : 
      61                 :            :                       /* The algorithm specified in the ELF ABI is as
      62                 :            :                          follows:
      63                 :            : 
      64                 :            :                          if (hi != 0)
      65                 :            :                          hash ^= hi >> 24;
      66                 :            : 
      67                 :            :                          hash &= ~hi;
      68                 :            : 
      69                 :            :                          But the following is equivalent and a lot
      70                 :            :                          faster, especially on modern processors.  */
      71                 :            : 
      72                 :       9384 :                       hash ^= hi;
      73                 :       9384 :                       hash ^= hi >> 24;
      74                 :            :                     }
      75                 :            :                 }
      76                 :            :             }
      77                 :            :         }
      78                 :            :     }
      79                 :      88832 :   return hash;
      80                 :            : }
      81                 :            : 
      82                 :            : #endif /* dl-hash.h */