xz_crc32.c (1261B)
1 /* 2 * CRC32 using the polynomial from IEEE-802.3 3 * 4 * Authors: Lasse Collin <lasse.collin@tukaani.org> 5 * Igor Pavlov <http://7-zip.org/> 6 * 7 * This file has been put into the public domain. 8 * You can do whatever you want with this file. 9 */ 10 11 /* 12 * This is not the fastest implementation, but it is pretty compact. 13 * The fastest versions of xz_crc32() on modern CPUs without hardware 14 * accelerated CRC instruction are 3-5 times as fast as this version, 15 * but they are bigger and use more memory for the lookup table. 16 */ 17 18 #include "xz_private.h" 19 20 /* 21 * STATIC_RW_DATA is used in the pre-boot environment on some architectures. 22 * See <linux/decompress/mm.h> for details. 23 */ 24 #ifndef STATIC_RW_DATA 25 # define STATIC_RW_DATA static 26 #endif 27 28 STATIC_RW_DATA uint32_t xz_crc32_table[256]; 29 30 XZ_EXTERN void xz_crc32_init(void) 31 { 32 const uint32_t poly = 0xEDB88320; 33 34 uint32_t i; 35 uint32_t j; 36 uint32_t r; 37 38 for (i = 0; i < 256; ++i) { 39 r = i; 40 for (j = 0; j < 8; ++j) 41 r = (r >> 1) ^ (poly & ~((r & 1) - 1)); 42 43 xz_crc32_table[i] = r; 44 } 45 46 return; 47 } 48 49 XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc) 50 { 51 crc = ~crc; 52 53 while (size != 0) { 54 crc = xz_crc32_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8); 55 --size; 56 } 57 58 return ~crc; 59 }