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author Nomad
date Fri, 05 Oct 2012 16:07:14 +0200
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1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-1998 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6 /* @(#) $Id$ */
7
8 #include "zlib.h"
9
10 #define local static
11
12 #ifdef DYNAMIC_CRC_TABLE
13
14 local int crc_table_empty = 1;
15 local uLongf crc_table[256];
16 local void make_crc_table OF((void));
17
18 /*
19 Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
20 x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
21
22 Polynomials over GF(2) are represented in binary, one bit per coefficient,
23 with the lowest powers in the most significant bit. Then adding polynomials
24 is just exclusive-or, and multiplying a polynomial by x is a right shift by
25 one. If we call the above polynomial p, and represent a byte as the
26 polynomial q, also with the lowest power in the most significant bit (so the
27 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
28 where a mod b means the remainder after dividing a by b.
29
30 This calculation is done using the shift-register method of multiplying and
31 taking the remainder. The register is initialized to zero, and for each
32 incoming bit, x^32 is added mod p to the register if the bit is a one (where
33 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
34 x (which is shifting right by one and adding x^32 mod p if the bit shifted
35 out is a one). We start with the highest power (least significant bit) of
36 q and repeat for all eight bits of q.
37
38 The table is simply the CRC of all possible eight bit values. This is all
39 the information needed to generate CRC's on data a byte at a time for all
40 combinations of CRC register values and incoming bytes.
41 */
42 local void make_crc_table()
43 {
44 uLong c;
45 int n, k;
46 uLong poly; /* polynomial exclusive-or pattern */
47 /* terms of polynomial defining this crc (except x^32): */
48 static const Byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
49
50 /* make exclusive-or pattern from polynomial (0xedb88320L) */
51 poly = 0L;
52 for (n = 0; n < sizeof(p)/sizeof(Byte); n++)
53 poly |= 1L << (31 - p[n]);
54
55 for (n = 0; n < 256; n++)
56 {
57 c = (uLong)n;
58 for (k = 0; k < 8; k++)
59 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
60 crc_table[n] = c;
61 }
62 crc_table_empty = 0;
63 }
64 #else
65 /* ========================================================================
66 * Table of CRC-32's of all single-byte values (made by make_crc_table)
67 */
68 local const uLongf crc_table[256] = {
69 0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
70 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
71 0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
72 0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
73 0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
74 0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
75 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
76 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
77 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
78 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
79 0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
80 0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
81 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
82 0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
83 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
84 0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
85 0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
86 0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
87 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
88 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
89 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
90 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
91 0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
92 0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
93 0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
94 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
95 0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
96 0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
97 0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
98 0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
99 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
100 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
101 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
102 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
103 0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
104 0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
105 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
106 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
107 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
108 0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
109 0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
110 0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
111 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
112 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
113 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
114 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
115 0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
116 0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
117 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
118 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
119 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
120 0x2d02ef8dL
121 };
122 #endif
123
124 /* =========================================================================
125 * This function can be used by asm versions of crc32()
126 */
127 const uLongf * ZEXPORT get_crc_table()
128 {
129 #ifdef DYNAMIC_CRC_TABLE
130 if (crc_table_empty) make_crc_table();
131 #endif
132 return (const uLongf *)crc_table;
133 }
134
135 /* ========================================================================= */
136 #define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
137 #define DO2(buf) DO1(buf); DO1(buf);
138 #define DO4(buf) DO2(buf); DO2(buf);
139 #define DO8(buf) DO4(buf); DO4(buf);
140
141 /* ========================================================================= */
142 uLong ZEXPORT crc32(crc, buf, len)
143 uLong crc;
144 const Bytef *buf;
145 uInt len;
146 {
147 if (buf == Z_NULL) return 0L;
148 #ifdef DYNAMIC_CRC_TABLE
149 if (crc_table_empty)
150 make_crc_table();
151 #endif
152 crc = crc ^ 0xffffffffL;
153 while (len >= 8)
154 {
155 DO8(buf);
156 len -= 8;
157 }
158 if (len) do {
159 DO1(buf);
160 } while (--len);
161 return crc ^ 0xffffffffL;
162 }