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