crc32.c revision 92114 
1/* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2002 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6#include <sys/cdefs.h>
7__FBSDID("$FreeBSD: head/lib/libz/crc32.c 92114 2002-03-11 22:36:26Z green $");
8
9#include "zlib.h"
10
11#define local static
12
13#ifdef DYNAMIC_CRC_TABLE
14
15local int crc_table_empty = 1;
16local uLongf crc_table[256];
17local void make_crc_table OF((void));
18
19/*
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.
22
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.
30
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.
38
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.
42*/
43local void make_crc_table()
44{
45  uLong c;
46  int n, k;
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};
50
51  /* make exclusive-or pattern from polynomial (0xedb88320L) */
52  poly = 0L;
53  for (n = 0; n < sizeof(p)/sizeof(Byte); n++)
54    poly |= 1L << (31 - p[n]);
55
56  for (n = 0; n < 256; n++)
57  {
58    c = (uLong)n;
59    for (k = 0; k < 8; k++)
60      c = c & 1 ? poly ^ (c >> 1) : c >> 1;
61    crc_table[n] = c;
62  }
63  crc_table_empty = 0;
64}
65#else
66/* ========================================================================
67 * Table of CRC-32's of all single-byte values (made by make_crc_table)
68 */
69local 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,
121  0x2d02ef8dL
122};
123#endif
124
125/* =========================================================================
126 * This function can be used by asm versions of crc32()
127 */
128const uLongf * ZEXPORT get_crc_table()
129{
130#ifdef DYNAMIC_CRC_TABLE
131  if (crc_table_empty) make_crc_table();
132#endif
133  return (const uLongf *)crc_table;
134}
135
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);
141
142/* ========================================================================= */
143uLong ZEXPORT crc32(crc, buf, len)
144    uLong crc;
145    const Bytef *buf;
146    uInt len;
147{
148    if (buf == Z_NULL) return 0L;
149#ifdef DYNAMIC_CRC_TABLE
150    if (crc_table_empty)
151      make_crc_table();
152#endif
153    crc = crc ^ 0xffffffffL;
154    while (len >= 8)
155    {
156      DO8(buf);
157      len -= 8;
158    }
159    if (len) do {
160      DO1(buf);
161    } while (--len);
162    return crc ^ 0xffffffffL;
163}
164