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76 lines
2.1 KiB
C
76 lines
2.1 KiB
C
/* Compute hash value for given string according to ELF standard.
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Copyright (C) 1995-2020 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef _DL_HASH_H
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#define _DL_HASH_H 1
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/* This is the hashing function specified by the ELF ABI. In the
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first five operations no overflow is possible so we optimized it a
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bit. */
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static unsigned int
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__attribute__ ((unused))
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_dl_elf_hash (const char *name_arg)
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{
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const unsigned char *name = (const unsigned char *) name_arg;
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unsigned long int hash = *name;
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if (hash != 0 && name[1] != '\0')
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{
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hash = (hash << 4) + name[1];
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if (name[2] != '\0')
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{
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hash = (hash << 4) + name[2];
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if (name[3] != '\0')
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{
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hash = (hash << 4) + name[3];
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if (name[4] != '\0')
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{
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hash = (hash << 4) + name[4];
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name += 5;
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while (*name != '\0')
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{
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unsigned long int hi;
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hash = (hash << 4) + *name++;
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hi = hash & 0xf0000000;
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/* The algorithm specified in the ELF ABI is as
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follows:
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if (hi != 0)
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hash ^= hi >> 24;
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hash &= ~hi;
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But the following is equivalent and a lot
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faster, especially on modern processors. */
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hash ^= hi >> 24;
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}
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/* Second part of the modified formula. This
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operation can be lifted outside the loop. */
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hash &= 0x0fffffff;
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}
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}
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}
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}
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return hash;
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}
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#endif /* dl-hash.h */
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