mirror of
git://sourceware.org/git/glibc.git
synced 2024-11-21 01:12:26 +08:00
76 lines
2.1 KiB
C
76 lines
2.1 KiB
C
/* Compute hash value for given string according to ELF standard.
|
|
Copyright (C) 1995-2020 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, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
#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__ ((unused))
|
|
_dl_elf_hash (const char *name_arg)
|
|
{
|
|
const unsigned char *name = (const unsigned char *) name_arg;
|
|
unsigned long int hash = *name;
|
|
if (hash != 0 && name[1] != '\0')
|
|
{
|
|
hash = (hash << 4) + name[1];
|
|
if (name[2] != '\0')
|
|
{
|
|
hash = (hash << 4) + name[2];
|
|
if (name[3] != '\0')
|
|
{
|
|
hash = (hash << 4) + name[3];
|
|
if (name[4] != '\0')
|
|
{
|
|
hash = (hash << 4) + name[4];
|
|
name += 5;
|
|
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 >> 24;
|
|
}
|
|
|
|
/* Second part of the modified formula. This
|
|
operation can be lifted outside the loop. */
|
|
hash &= 0x0fffffff;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
return hash;
|
|
}
|
|
|
|
#endif /* dl-hash.h */
|