/* crc32.c -- compute the CRC-32 of a data stream

 * Copyright (C) 1995-1998 Mark Adler

 * For conditions of distribution and use, see copyright notice in zlib.h 

 */

/* @(#) $Id$ */

#include "zlib.h"

#define local static

#ifdef DYNAMIC_CRC_TABLE

local int crc_table_empty = 1;

local uLongf crc_table[256];

local void make_crc_table OF((void));

/*

  Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:

  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.

  Polynomials over GF(2) are represented in binary, one bit per coefficient,

  with the lowest powers in the most significant bit.  Then adding polynomials

  is just exclusive-or, and multiplying a polynomial by x is a right shift by

  one.  If we call the above polynomial p, and represent a byte as the

  polynomial q, also with the lowest power in the most significant bit (so the

  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,

  where a mod b means the remainder after dividing a by b.

  This calculation is done using the shift-register method of multiplying and

  taking the remainder.  The register is initialized to zero, and for each

  incoming bit, x^32 is added mod p to the register if the bit is a one (where

  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by

  x (which is shifting right by one and adding x^32 mod p if the bit shifted

  out is a one).  We start with the highest power (least significant bit) of

  q and repeat for all eight bits of q.

  The table is simply the CRC of all possible eight bit values.  This is all

  the information needed to generate CRC's on data a byte at a time for all

  combinations of CRC register values and incoming bytes.

*/

local void make_crc_table()

{

  uLong c;

  int n, k;

  uLong poly;            /* polynomial exclusive-or pattern */

  /* terms of polynomial defining this crc (except x^32): */

  static const Byte p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

  /* make exclusive-or pattern from polynomial (0xedb88320L) */

  poly = 0L;

  for (n = 0; n < sizeof(p)/sizeof(Byte); n++)

    poly |= 1L << (31 - p[n]);

  for (n = 0; n < 256; n++)

  {

    c = (uLong)n;

    for (k = 0; k < 8; k++)

      c = c & 1 ? poly ^ (c >> 1) : c >> 1;

    crc_table[n] = c;

  }

  crc_table_empty = 0;

}

#else

/* ========================================================================

 * Table of CRC-32's of all single-byte values (made by make_crc_table)

 */

local const uLongf crc_table[256] = {

  0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,

  0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,

  0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,

  0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,

  0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,

  0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,

  0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,

  0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,

  0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,

  0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,

  0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,

  0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,

  0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,

  0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,

  0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,

  0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,

  0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,

  0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,

  0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,

  0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,

  0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,

  0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,

  0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,

  0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,

  0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,

  0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,

  0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,

  0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,

  0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,

  0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,

  0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,

  0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,

  0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,

  0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,

  0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,

  0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,

  0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,

  0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,

  0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,

  0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,

  0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,

  0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,

  0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,

  0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,

  0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,

  0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,

  0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,

  0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,

  0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,

  0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,

  0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,

  0x2d02ef8dL

};

#endif

/* =========================================================================

 * This function can be used by asm versions of crc32()

 */

const uLongf * ZEXPORT get_crc_table()

{

#ifdef DYNAMIC_CRC_TABLE

  if (crc_table_empty) make_crc_table();

#endif

  return (const uLongf *)crc_table;

}

/* ========================================================================= */

#define DO1(buf) crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);

#define DO2(buf)  DO1(buf); DO1(buf);

#define DO4(buf)  DO2(buf); DO2(buf);

#define DO8(buf)  DO4(buf); DO4(buf);

/* ========================================================================= */

uLong ZEXPORT crc32(uLong crc, const Bytef *buf, uInt len)

{

    if (buf == Z_NULL) return 0L;

#ifdef DYNAMIC_CRC_TABLE

    if (crc_table_empty)

      make_crc_table();

#endif

    crc = crc ^ 0xffffffffL;

    while (len >= 8)

    {

      DO8(buf);

      len -= 8;

    }

    if (len) do {

      DO1(buf);

    } while (--len);

    return crc ^ 0xffffffffL;

}