File: crctab.c

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/* crctab.c -- supply the CRC table needed for CRC-32 calculations.
 * Copyright (C) 1995 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* $Id: crctab.c,v 1.4 1996/01/08 14:55:12 jloup Exp $ */

/*
  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.
*/

#include "zip.h"

#if (!defined(USE_ZLIB) || defined(USE_OWN_CRCTAB))

#ifndef ZCONST
#  define ZCONST const
#endif

#ifdef DYNAMIC_CRC_TABLE

/* =========================================================================
 * Make the crc table. This function is needed only if you want to compute
 * the table dynamically.
 */

local void make_crc_table OF((void));

#if (defined(DYNALLOC_CRCTAB) && defined(REENTRANT))
   error: Dynamic allocation of CRC table not safe with reentrant code.
#endif /* DYNALLOC && REENTRANT */

#ifdef DYNALLOC_CRCTAB
   local ulg near *crc_table = NULL;
# if 0          /* not used, since sizeof("near *") <= sizeof(int) */
   /* Use this section when access to a "local int" is faster than access to
      a "local pointer" (e.g.: i86 16bit code with far pointers). */
   local int crc_table_empty = 1;
#  define CRC_TABLE_IS_EMPTY    (crc_table_empty != 0)
#  define MARK_CRCTAB_FILLED    crc_table_empty = 0
#  define MARK_CRCTAB_EMPTY     crc_table_empty = 1
# else
   /* Use this section on systems where the size of pointers and ints is
      equal (e.g.: all 32bit systems). */
#  define CRC_TABLE_IS_EMPTY    (crc_table == NULL)
#  define MARK_CRCTAB_FILLED    crc_table = crctab_p
#  define MARK_CRCTAB_EMPTY     crc_table = NULL
# endif
#else /* !DYNALLOC_CRCTAB */
   local ulg near crc_table[256];
   local int crc_table_empty = 1;
#  define CRC_TABLE_IS_EMPTY    (crc_table_empty != 0)
#  define MARK_CRCTAB_FILLED    crc_table_empty = 0
#endif /* ?DYNALLOC_CRCTAB */


local void make_crc_table()
{
  ulg c;                /* crc shift register */
  int n;                /* counter for all possible eight bit values */
  int k;                /* byte being shifted into crc apparatus */
#ifdef DYNALLOC_CRCTAB
  ulg near *crctab_p;   /* temporary pointer to allocated crc_table area */
#else /* !DYNALLOC_CRCTAB */
# define crctab_p crc_table
#endif /* DYNALLOC_CRCTAB */

#ifdef COMPUTE_XOR_PATTERN
  /* This piece of code has been left here to explain how the XOR pattern
   * used in the creation of the crc_table values can be recomputed.
   * For production versions of this function, it is more efficient to
   * supply the resultant pattern at compile time.
   */
  ulg xor;              /* polynomial exclusive-or pattern */
  /* terms of polynomial defining this crc (except x^32): */
  static uch p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};

  /* make exclusive-or pattern from polynomial (0xedb88320L) */
  xor = 0L;
  for (i = 0; i < sizeof(p)/sizeof(uch); i++)
    xor |= 1L << (31 - p[i]);
#else
# define xor 0xedb88320L
#endif

#ifdef DYNALLOC_CRCTAB
  crctab_p = (ulg near *) nearmalloc (256*sizeof(ulg));
  if (crctab_p == NULL) {
    ziperr(ZE_MEM, "crc_table allocation");
  }
#endif /* DYNALLOC_CRCTAB */

  for (n = 0; n < 256; n++) {
    c = (ulg)n;
    for (k = 8; k; k--)
      c = c & 1 ? xor ^ (c >> 1) : c >> 1;
    crctab_p[n] = c;
  }
  MARK_CRCTAB_FILLED;
}

#else /* !DYNAMIC_CRC_TABLE */

#ifdef DYNALLOC_CRCTAB
   error: Inconsistent flags, DYNALLOC_CRCTAB without DYNAMIC_CRC_TABLE.
#endif

/* ========================================================================
 * Table of CRC-32's of all single-byte values (made by make_crc_table)
 */
local ZCONST ulg near crc_table[] = {
  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 /* ?DYNAMIC_CRC_TABLE */

#ifdef USE_ZLIB
uLongf *get_crc_table()
#else
ulg near *get_crc_table()
#endif
{
#ifdef DYNAMIC_CRC_TABLE
  if (CRC_TABLE_IS_EMPTY)
    make_crc_table();
#endif
#ifdef USE_ZLIB
  return (uLongf *)crc_table;
#else
  return (ulg near *)crc_table;
#endif
}

#ifdef DYNALLOC_CRCTAB
void free_crc_table()
{
  if (!CRC_TABLE_IS_EMPTY)
  {
    nearfree((ulg near *)crc_table);
    MARK_CRCTAB_EMPTY;
  }
}
#endif

#endif /* !USE_ZLIB || USE_OWN_CRCTAB */