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Copyright (c) 1990-2000 Info-ZIP. All rights reserved.
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See the accompanying file LICENSE, version 2000-Apr-09 or later
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(the contents of which are also included in zip.h) for terms of use.
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If, for some reason, all these files are missing, the Info-ZIP license
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also may be found at: ftp://ftp.info-zip.org/pub/infozip/license.html
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/* crctab.c -- supply the CRC table needed for CRC-32 calculations.
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* Copyright (C) 1995 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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/* $Id: crctab.c,v 1.4 1996/01/08 14:55:12 jloup Exp $ */
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Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
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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.
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Polynomials over GF(2) are represented in binary, one bit per coefficient,
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with the lowest powers in the most significant bit. Then adding polynomials
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is just exclusive-or, and multiplying a polynomial by x is a right shift by
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one. If we call the above polynomial p, and represent a byte as the
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polynomial q, also with the lowest power in the most significant bit (so the
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byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
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where a mod b means the remainder after dividing a by b.
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This calculation is done using the shift-register method of multiplying and
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taking the remainder. The register is initialized to zero, and for each
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incoming bit, x^32 is added mod p to the register if the bit is a one (where
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x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
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x (which is shifting right by one and adding x^32 mod p if the bit shifted
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out is a one). We start with the highest power (least significant bit) of
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q and repeat for all eight bits of q.
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The table is simply the CRC of all possible eight bit values. This is all
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the information needed to generate CRC's on data a byte at a time for all
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combinations of CRC register values and incoming bytes.
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#define __CRCTAB_C /* identifies this source module */
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#if (!defined(USE_ZLIB) || defined(USE_OWN_CRCTAB))
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#ifdef DYNAMIC_CRC_TABLE
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/* =========================================================================
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* Make the crc table. This function is needed only if you want to compute
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* the table dynamically.
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local void make_crc_table OF((void));
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#if (defined(DYNALLOC_CRCTAB) && defined(REENTRANT))
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error: Dynamic allocation of CRC table not safe with reentrant code.
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#endif /* DYNALLOC_CRCTAB && REENTRANT */
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#ifdef DYNALLOC_CRCTAB
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local ulg near *crc_table = NULL;
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# if 0 /* not used, since sizeof("near *") <= sizeof(int) */
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/* Use this section when access to a "local int" is faster than access to
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a "local pointer" (e.g.: i86 16bit code with far pointers). */
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local int crc_table_empty = 1;
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# define CRC_TABLE_IS_EMPTY (crc_table_empty != 0)
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# define MARK_CRCTAB_FILLED crc_table_empty = 0
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# define MARK_CRCTAB_EMPTY crc_table_empty = 1
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/* Use this section on systems where the size of pointers and ints is
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equal (e.g.: all 32bit systems). */
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# define CRC_TABLE_IS_EMPTY (crc_table == NULL)
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# define MARK_CRCTAB_FILLED crc_table = crctab_p
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# define MARK_CRCTAB_EMPTY crc_table = NULL
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#else /* !DYNALLOC_CRCTAB */
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local ulg near crc_table[256];
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local int crc_table_empty = 1;
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# define CRC_TABLE_IS_EMPTY (crc_table_empty != 0)
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# define MARK_CRCTAB_FILLED crc_table_empty = 0
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#endif /* ?DYNALLOC_CRCTAB */
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local void make_crc_table()
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ulg c; /* crc shift register */
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int n; /* counter for all possible eight bit values */
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int k; /* byte being shifted into crc apparatus */
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#ifdef DYNALLOC_CRCTAB
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ulg near *crctab_p; /* temporary pointer to allocated crc_table area */
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#else /* !DYNALLOC_CRCTAB */
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# define crctab_p crc_table
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#endif /* DYNALLOC_CRCTAB */
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#ifdef COMPUTE_XOR_PATTERN
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/* This piece of code has been left here to explain how the XOR pattern
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* used in the creation of the crc_table values can be recomputed.
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* For production versions of this function, it is more efficient to
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* supply the resultant pattern at compile time.
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ulg xor; /* polynomial exclusive-or pattern */
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/* terms of polynomial defining this crc (except x^32): */
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static uch p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
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/* make exclusive-or pattern from polynomial (0xedb88320L) */
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for (i = 0; i < sizeof(p)/sizeof(uch); i++)
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xor |= 1L << (31 - p[i]);
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# define xor 0xedb88320L
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#ifdef DYNALLOC_CRCTAB
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crctab_p = (ulg near *) nearmalloc (256*sizeof(ulg));
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if (crctab_p == NULL) {
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ziperr(ZE_MEM, "crc_table allocation");
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#endif /* DYNALLOC_CRCTAB */
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for (n = 0; n < 256; n++) {
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c = c & 1 ? xor ^ (c >> 1) : c >> 1;
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#else /* !DYNAMIC_CRC_TABLE */
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#ifdef DYNALLOC_CRCTAB
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error: Inconsistent flags, DYNALLOC_CRCTAB without DYNAMIC_CRC_TABLE.
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/* ========================================================================
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* Table of CRC-32's of all single-byte values (made by make_crc_table)
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local ZCONST ulg near crc_table[256] = {
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0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
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0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
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0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
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0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
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0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
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0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
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0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
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0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
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0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
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0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
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0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
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0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
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0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
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0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
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0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
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0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
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0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
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0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
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0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
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0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
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0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
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0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
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0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
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0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
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0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
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0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
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0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
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0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
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0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
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0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
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0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
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0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
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0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
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0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
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0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
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0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
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0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
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0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
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0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
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0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
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0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
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0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
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0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
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0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
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0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
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0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
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0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
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0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
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0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
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0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
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0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
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#endif /* ?DYNAMIC_CRC_TABLE */
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/* use "OF((void))" here to work around a Borland TC++ 1.0 problem */
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ZCONST uLongf *get_crc_table OF((void))
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ZCONST ulg near *get_crc_table OF((void))
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#ifdef DYNAMIC_CRC_TABLE
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if (CRC_TABLE_IS_EMPTY)
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return (ZCONST uLongf *)crc_table;
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return (ZCONST ulg near *)crc_table;
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#ifdef DYNALLOC_CRCTAB
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void free_crc_table()
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if (!CRC_TABLE_IS_EMPTY)
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nearfree((ulg near *)crc_table);
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#endif /* !USE_ZLIB || USE_OWN_CRCTAB */
added
removed
crctab.c
