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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. */ 26 : : static unsigned int 27 : : __attribute__ ((unused)) 28 : 178688 : _dl_elf_hash (const char *name_arg) 29 : : { 30 : 178688 : const unsigned char *name = (const unsigned char *) name_arg; 31 : 178688 : unsigned long int hash = *name; 32 [ + - + + ]: 178688 : if (hash != 0 && name[1] != '\0') 33 : : { 34 : 178644 : hash = (hash << 4) + name[1]; 35 [ + + ]: 178644 : if (name[2] != '\0') 36 : : { 37 : 178282 : hash = (hash << 4) + name[2]; 38 [ + + ]: 178282 : if (name[3] != '\0') 39 : : { 40 : 174648 : hash = (hash << 4) + name[3]; 41 [ + + ]: 174648 : if (name[4] != '\0') 42 : : { 43 : 138612 : hash = (hash << 4) + name[4]; 44 : 138612 : name += 5; 45 [ + + ]: 163916 : while (*name != '\0') 46 : : { 47 : 25304 : unsigned long int hi; 48 : 25304 : hash = (hash << 4) + *name++; 49 : 25304 : 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 : 25304 : hash ^= hi >> 24; 63 : : } 64 : : 65 : : /* Second part of the modified formula. This 66 : : operation can be lifted outside the loop. */ 67 : 138612 : hash &= 0x0fffffff; 68 : : } 69 : : } 70 : : } 71 : : } 72 : 178688 : return hash; 73 : : } 74 : : 75 : : #endif /* dl-hash.h */