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 _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
