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glibc/sysdeps/generic/dl-hash.h
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/* Compute hash value for given string according to ELF standard. | |
Copyright (C) 1995-1998,2003,2005,2011 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 | |
__attribute__ ((used)) | |
_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 */ |