1/* Compute hash value for given string according to ELF standard.
2   Copyright (C) 1995-2015 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, see
17   <http://www.gnu.org/licenses/>.  */
18
19#ifndef _DL_HASH_H
20#define _DL_HASH_H	1
21
22
23/* This is the hashing function specified by the ELF ABI.  In the
24   first five operations no overflow is possible so we optimized it a
25   bit.  */
26static unsigned int
27__attribute__ ((unused))
28_dl_elf_hash (const char *name_arg)
29{
30  const unsigned char *name = (const unsigned char *) name_arg;
31  unsigned long int hash = *name;
32  if (hash != 0 && name[1] != '\0')
33    {
34      hash = (hash << 4) + name[1];
35      if (name[2] != '\0')
36	{
37	  hash = (hash << 4) + name[2];
38	  if (name[3] != '\0')
39	    {
40	      hash = (hash << 4) + name[3];
41	      if (name[4] != '\0')
42		{
43		  hash = (hash << 4) + name[4];
44		  name += 5;
45		  while (*name != '\0')
46		    {
47		      unsigned long int hi;
48		      hash = (hash << 4) + *name++;
49		      hi = hash & 0xf0000000;
50
51		      /* The algorithm specified in the ELF ABI is as
52			 follows:
53
54			 if (hi != 0)
55			   hash ^= hi >> 24;
56
57			 hash &= ~hi;
58
59			 But the following is equivalent and a lot
60			 faster, especially on modern processors.  */
61
62		      hash ^= hi >> 24;
63		    }
64
65		  /* Second part of the modified formula.  This
66		     operation can be lifted outside the loop.  */
67		  hash &= 0x0fffffff;
68		}
69	    }
70	}
71    }
72  return hash;
73}
74
75#endif /* dl-hash.h */
76