crc32.c

   1 /*
   2  * The implementation here was originally done by Gary S. Brown.
   3  * I have borrowed the tables directly, and made some minor changes
   4  * to the crc32-function (including changing the interface).
   5  * //ylo
   6  */
   7
   8 #include "includes.h"
   9 RCSID("$OpenBSD: crc32.c,v 1.6 2000/08/19 02:17:12 deraadt Exp $");
  10
  11 #include "crc32.h"
  12
  13   /* ============================================================= */
  14   /*  COPYRIGHT (C) 1986 Gary S. Brown.  You may use this program, or       */
  15   /*  code or tables extracted from it, as desired without restriction.     */
  16   /*                                                                        */
  17   /*  First, the polynomial itself and its table of feedback terms.  The    */
  18   /*  polynomial is                                                         */
  19   /*  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+X^0   */
  20   /*                                                                        */
  21   /*  Note that we take it "backwards" and put the highest-order term in    */
  22   /*  the lowest-order bit.  The X^32 term is "implied"; the LSB is the     */
  23   /*  X^31 term, etc.  The X^0 term (usually shown as "+1") results in      */
  24   /*  the MSB being 1.                                                      */
  25   /*                                                                        */
  26   /*  Note that the usual hardware shift register implementation, which     */
  27   /*  is what we're using (we're merely optimizing it by doing eight-bit    */
  28   /*  chunks at a time) shifts bits into the lowest-order term.  In our     */
  29   /*  implementation, that means shifting towards the right.  Why do we     */
  30   /*  do it this way?  Because the calculated CRC must be transmitted in    */
  31   /*  order from highest-order term to lowest-order term.  UARTs transmit   */
  32   /*  characters in order from LSB to MSB.  By storing the CRC this way,    */
  33   /*  we hand it to the UART in the order low-byte to high-byte; the UART   */
  34   /*  sends each low-bit to hight-bit; and the result is transmission bit   */
  35   /*  by bit from highest- to lowest-order term without requiring any bit   */
  36   /*  shuffling on our part.  Reception works similarly.                    */
  37   /*                                                                        */
  38   /*  The feedback terms table consists of 256, 32-bit entries.  Notes:     */
  39   /*                                                                        */
  40   /*      The table can be generated at runtime if desired; code to do so   */
  41   /*      is shown later.  It might not be obvious, but the feedback        */
  42   /*      terms simply represent the results of eight shift/xor opera-      */
  43   /*      tions for all combinations of data and CRC register values.       */
  44   /*                                                                        */
  45   /*      The values must be right-shifted by eight bits by the "updcrc"    */
  46   /*      logic; the shift must be unsigned (bring in zeroes).  On some     */
  47   /*      hardware you could probably optimize the shift in assembler by    */
  48   /*      using byte-swap instructions.                                     */
  49   /*      polynomial $edb88320                                              */
  50   /*                                                                        */
  51   /*  --------------------------------------------------------------------  */
  52
  53 static unsigned int crc32_tab[] = {
  54         0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
  55         0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
  56         0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
  57         0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
  58         0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
  59         0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
  60         0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
  61         0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
  62         0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
  63         0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
  64         0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
  65         0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
  66         0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
  67         0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
  68         0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
  69         0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
  70         0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
  71         0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
  72         0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
  73         0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
  74         0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
  75         0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
  76         0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
  77         0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
  78         0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
  79         0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
  80         0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
  81         0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
  82         0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
  83         0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
  84         0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
  85         0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
  86         0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
  87         0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
  88         0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
  89         0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
  90         0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
  91         0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
  92         0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
  93         0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
  94         0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
  95         0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
  96         0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
  97         0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
  98         0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
  99         0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
 100         0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
 101         0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
 102         0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
 103         0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
 104         0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
 105         0x2d02ef8dL
 106 };
 107
 108 /* Return a 32-bit CRC of the contents of the buffer. */
 109
 110 unsigned int
 111 ssh_crc32(const unsigned char *s, unsigned int len)
 112 {
 113         unsigned int i;
 114         unsigned int crc32val;
 115
 116         crc32val = 0;
 117         for (i = 0;  i < len;  i ++) {
 118                 crc32val = crc32_tab[(crc32val ^ s[i]) & 0xff] ^ (crc32val >> 8);
 119         }
 120         return crc32val;
 121 }