1 /* 2 * efone - Distributed internet phone system. 3 * 4 * (c) 1999,2000 Krzysztof Dabrowski 5 * (c) 1999,2000 ElysiuM deeZine 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public License 9 * as published by the Free Software Foundation; either version 10 * 2 of the License, or (at your option) any later version. 11 * 12 */ 13 14 /* based on implementation by Finn Yannick Jacobs */ 15 16 #include <stdio.h> 17 #include <stdlib.h> 18 #include <sys/types.h> 19 #include "crc32.h" 20 21 /* crc_tab[] -- this crcTable is being build by chksum_crc32GenTab(). 22 * so make sure, you call it before using the other 23 * functions! 24 */ 25 uint32_t crc_tab[256]; 26 27 /* chksum_crc() -- to a given block, this one calculates the 28 * crc32-checksum until the length is 29 * reached. the crc32-checksum will be 30 * the result. 31 */ 32 uint32_t chksum_crc32 (unsigned char *block, unsigned int length) 33 { 34 unsigned long crc; 35 unsigned long i; 36 37 crc = 0xFFFFFFFF; 38 for (i = 0; i < length; i++) 39 { 40 crc = ((crc >> 8) & 0x00FFFFFF) ^ crc_tab[(crc ^ *block++) & 0xFF]; 41 } 42 return (crc ^ 0xFFFFFFFF); 43 } 44 45 /* chksum_crc32gentab() -- to a global crc_tab[256], this one will 46 * calculate the crcTable for crc32-checksums. 47 * it is generated to the polynom [..] 48 */ 49 50 void chksum_crc32gentab () 51 { 52 unsigned long crc, poly; 53 int i, j; 54 55 poly = 0xEDB88320L; 56 for (i = 0; i < 256; i++) 57 { 58 crc = i; 59 for (j = 8; j > 0; j--) 60 { 61 if (crc & 1) 62 { 63 crc = (crc >> 1) ^ poly; 64 } 65 else 66 { 67 crc >>= 1; 68 } 69 } 70 crc_tab[i] = crc; 71 } 72 } 73
