zlib/crc32.c

   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 /* @(#) $Id: crc32.c,v 1.3 2002/03/11 22:11:16 tromey Exp $ */
   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 }