| 1 | /* crc32.c -- compute the CRC-32 of a data stream
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| 2 | * Copyright (C) 1995-2005 Mark Adler
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| 3 | * For conditions of distribution and use, see copyright notice in zlib.h
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| 4 | *
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| 5 | * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
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| 6 | * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
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| 7 | * tables for updating the shift register in one step with three exclusive-ors
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| 8 | * instead of four steps with four exclusive-ors. This results in about a
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| 9 | * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
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| 10 | */
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| 11 |
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| 12 | /* @(#) $Id: crc32.c,v 1.1 2005/09/23 22:39:00 beng Exp $ */
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| 13 |
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| 14 | /*
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| 15 | Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
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| 16 | protection on the static variables used to control the first-use generation
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| 17 | of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
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| 18 | first call get_crc_table() to initialize the tables before allowing more than
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| 19 | one thread to use crc32().
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| 20 | */
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| 21 |
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| 22 | #ifdef MAKECRCH
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| 23 | # include <stdio.h>
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| 24 | # ifndef DYNAMIC_CRC_TABLE
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| 25 | # define DYNAMIC_CRC_TABLE
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| 26 | # endif /* !DYNAMIC_CRC_TABLE */
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| 27 | #endif /* MAKECRCH */
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| 28 |
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| 29 | #include "zutil.h" /* for STDC and FAR definitions */
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| 30 |
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| 31 | #define local static
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| 32 |
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| 33 | /* Find a four-byte integer type for crc32_little() and crc32_big(). */
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| 34 | #ifndef NOBYFOUR
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| 35 | # ifdef STDC /* need ANSI C limits.h to determine sizes */
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| 36 | # include <limits.h>
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| 37 | # define BYFOUR
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| 38 | # if (UINT_MAX == 0xffffffffUL)
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| 39 | typedef unsigned int u4;
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| 40 | # else
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| 41 | # if (ULONG_MAX == 0xffffffffUL)
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| 42 | typedef unsigned long u4;
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| 43 | # else
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| 44 | # if (USHRT_MAX == 0xffffffffUL)
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| 45 | typedef unsigned short u4;
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| 46 | # else
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| 47 | # undef BYFOUR /* can't find a four-byte integer type! */
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| 48 | # endif
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| 49 | # endif
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| 50 | # endif
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| 51 | # endif /* STDC */
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| 52 | #endif /* !NOBYFOUR */
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| 53 |
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| 54 | /* Definitions for doing the crc four data bytes at a time. */
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| 55 | #ifdef BYFOUR
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| 56 | # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
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| 57 | (((w)&0xff00)<<8)+(((w)&0xff)<<24))
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| 58 | local unsigned long crc32_little OF((unsigned long,
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| 59 | const unsigned char FAR *, unsigned));
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| 60 | local unsigned long crc32_big OF((unsigned long,
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| 61 | const unsigned char FAR *, unsigned));
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| 62 | # define TBLS 8
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| 63 | #else
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| 64 | # define TBLS 1
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| 65 | #endif /* BYFOUR */
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| 66 |
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| 67 | /* Local functions for crc concatenation */
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| 68 | local unsigned long gf2_matrix_times OF((unsigned long *mat,
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| 69 | unsigned long vec));
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| 70 | local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
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| 71 |
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| 72 | #ifdef DYNAMIC_CRC_TABLE
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| 73 |
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| 74 | local volatile int crc_table_empty = 1;
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| 75 | local unsigned long FAR crc_table[TBLS][256];
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| 76 | local void make_crc_table OF((void));
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| 77 | #ifdef MAKECRCH
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| 78 | local void write_table OF((FILE *, const unsigned long FAR *));
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| 79 | #endif /* MAKECRCH */
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| 80 | /*
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| 81 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
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| 82 | 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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| 83 |
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| 84 | Polynomials over GF(2) are represented in binary, one bit per coefficient,
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| 85 | with the lowest powers in the most significant bit. Then adding polynomials
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| 86 | is just exclusive-or, and multiplying a polynomial by x is a right shift by
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| 87 | one. If we call the above polynomial p, and represent a byte as the
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| 88 | polynomial q, also with the lowest power in the most significant bit (so the
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| 89 | byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
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| 90 | where a mod b means the remainder after dividing a by b.
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| 91 |
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| 92 | This calculation is done using the shift-register method of multiplying and
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| 93 | taking the remainder. The register is initialized to zero, and for each
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| 94 | incoming bit, x^32 is added mod p to the register if the bit is a one (where
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| 95 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
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| 96 | x (which is shifting right by one and adding x^32 mod p if the bit shifted
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| 97 | out is a one). We start with the highest power (least significant bit) of
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| 98 | q and repeat for all eight bits of q.
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| 99 |
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| 100 | The first table is simply the CRC of all possible eight bit values. This is
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| 101 | all the information needed to generate CRCs on data a byte at a time for all
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| 102 | combinations of CRC register values and incoming bytes. The remaining tables
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| 103 | allow for word-at-a-time CRC calculation for both big-endian and little-
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| 104 | endian machines, where a word is four bytes.
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| 105 | */
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| 106 | local void make_crc_table()
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| 107 | {
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| 108 | unsigned long c;
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| 109 | int n, k;
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| 110 | unsigned long poly; /* polynomial exclusive-or pattern */
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| 111 | /* terms of polynomial defining this crc (except x^32): */
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| 112 | static volatile int first = 1; /* flag to limit concurrent making */
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| 113 | static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
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| 114 |
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| 115 | /* See if another task is already doing this (not thread-safe, but better
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| 116 | than nothing -- significantly reduces duration of vulnerability in
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| 117 | case the advice about DYNAMIC_CRC_TABLE is ignored) */
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| 118 | if (first) {
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| 119 | first = 0;
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| 120 |
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| 121 | /* make exclusive-or pattern from polynomial (0xedb88320UL) */
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| 122 | poly = 0UL;
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| 123 | for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
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| 124 | poly |= 1UL << (31 - p[n]);
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| 125 |
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| 126 | /* generate a crc for every 8-bit value */
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| 127 | for (n = 0; n < 256; n++) {
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| 128 | c = (unsigned long)n;
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| 129 | for (k = 0; k < 8; k++)
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| 130 | c = c & 1 ? poly ^ (c >> 1) : c >> 1;
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| 131 | crc_table[0][n] = c;
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| 132 | }
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| 133 |
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| 134 | #ifdef BYFOUR
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| 135 | /* generate crc for each value followed by one, two, and three zeros,
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| 136 | and then the byte reversal of those as well as the first table */
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| 137 | for (n = 0; n < 256; n++) {
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| 138 | c = crc_table[0][n];
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| 139 | crc_table[4][n] = REV(c);
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| 140 | for (k = 1; k < 4; k++) {
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| 141 | c = crc_table[0][c & 0xff] ^ (c >> 8);
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| 142 | crc_table[k][n] = c;
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| 143 | crc_table[k + 4][n] = REV(c);
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| 144 | }
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| 145 | }
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| 146 | #endif /* BYFOUR */
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| 147 |
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| 148 | crc_table_empty = 0;
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| 149 | }
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| 150 | else { /* not first */
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| 151 | /* wait for the other guy to finish (not efficient, but rare) */
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| 152 | while (crc_table_empty)
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| 153 | ;
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| 154 | }
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| 155 |
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| 156 | #ifdef MAKECRCH
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| 157 | /* write out CRC tables to crc32.h */
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| 158 | {
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| 159 | FILE *out;
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| 160 |
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| 161 | out = fopen("crc32.h", "w");
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| 162 | if (out == NULL) return;
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| 163 | fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
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| 164 | fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
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| 165 | fprintf(out, "local const unsigned long FAR ");
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| 166 | fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
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| 167 | write_table(out, crc_table[0]);
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| 168 | # ifdef BYFOUR
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| 169 | fprintf(out, "#ifdef BYFOUR\n");
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| 170 | for (k = 1; k < 8; k++) {
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| 171 | fprintf(out, " },\n {\n");
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| 172 | write_table(out, crc_table[k]);
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| 173 | }
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| 174 | fprintf(out, "#endif\n");
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| 175 | # endif /* BYFOUR */
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| 176 | fprintf(out, " }\n};\n");
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| 177 | fclose(out);
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| 178 | }
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| 179 | #endif /* MAKECRCH */
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| 180 | }
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| 181 |
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| 182 | #ifdef MAKECRCH
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| 183 | local void write_table(out, table)
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| 184 | FILE *out;
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| 185 | const unsigned long FAR *table;
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| 186 | {
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| 187 | int n;
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| 188 |
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| 189 | for (n = 0; n < 256; n++)
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| 190 | fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
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| 191 | n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
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| 192 | }
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| 193 | #endif /* MAKECRCH */
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| 194 |
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| 195 | #else /* !DYNAMIC_CRC_TABLE */
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| 196 | /* ========================================================================
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| 197 | * Tables of CRC-32s of all single-byte values, made by make_crc_table().
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| 198 | */
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| 199 | #include "crc32.h"
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| 200 | #endif /* DYNAMIC_CRC_TABLE */
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| 201 |
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| 202 | /* =========================================================================
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| 203 | * This function can be used by asm versions of crc32()
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| 204 | */
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| 205 | const unsigned long FAR * ZEXPORT get_crc_table()
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| 206 | {
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| 207 | #ifdef DYNAMIC_CRC_TABLE
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| 208 | if (crc_table_empty)
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| 209 | make_crc_table();
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| 210 | #endif /* DYNAMIC_CRC_TABLE */
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| 211 | return (const unsigned long FAR *)crc_table;
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| 212 | }
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| 213 |
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| 214 | /* ========================================================================= */
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| 215 | #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
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| 216 | #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
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| 217 |
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| 218 | /* ========================================================================= */
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| 219 | unsigned long ZEXPORT crc32(crc, buf, len)
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| 220 | unsigned long crc;
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| 221 | const unsigned char FAR *buf;
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| 222 | unsigned len;
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| 223 | {
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| 224 | if (buf == Z_NULL) return 0UL;
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| 225 |
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| 226 | #ifdef DYNAMIC_CRC_TABLE
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| 227 | if (crc_table_empty)
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| 228 | make_crc_table();
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| 229 | #endif /* DYNAMIC_CRC_TABLE */
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| 230 |
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| 231 | #ifdef BYFOUR
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| 232 | if (sizeof(void *) == sizeof(ptrdiff_t)) {
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| 233 | u4 endian;
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| 234 |
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| 235 | endian = 1;
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| 236 | if (*((unsigned char *)(&endian)))
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| 237 | return crc32_little(crc, buf, len);
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| 238 | else
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| 239 | return crc32_big(crc, buf, len);
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| 240 | }
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| 241 | #endif /* BYFOUR */
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| 242 | crc = crc ^ 0xffffffffUL;
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| 243 | while (len >= 8) {
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| 244 | DO8;
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| 245 | len -= 8;
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| 246 | }
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| 247 | if (len) do {
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| 248 | DO1;
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| 249 | } while (--len);
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| 250 | return crc ^ 0xffffffffUL;
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| 251 | }
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| 252 |
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| 253 | #ifdef BYFOUR
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| 254 |
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| 255 | /* ========================================================================= */
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| 256 | #define DOLIT4 c ^= *buf4++; \
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| 257 | c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
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| 258 | crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
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| 259 | #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
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| 260 |
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| 261 | /* ========================================================================= */
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| 262 | local unsigned long crc32_little(crc, buf, len)
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| 263 | unsigned long crc;
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| 264 | const unsigned char FAR *buf;
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| 265 | unsigned len;
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| 266 | {
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| 267 | register u4 c;
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| 268 | register const u4 FAR *buf4;
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| 269 |
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| 270 | c = (u4)crc;
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| 271 | c = ~c;
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| 272 | while (len && ((ptrdiff_t)buf & 3)) {
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| 273 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
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| 274 | len--;
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| 275 | }
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| 276 |
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| 277 | buf4 = (const u4 FAR *)(const void FAR *)buf;
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| 278 | while (len >= 32) {
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| 279 | DOLIT32;
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| 280 | len -= 32;
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| 281 | }
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| 282 | while (len >= 4) {
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| 283 | DOLIT4;
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| 284 | len -= 4;
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| 285 | }
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| 286 | buf = (const unsigned char FAR *)buf4;
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| 287 |
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| 288 | if (len) do {
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| 289 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
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| 290 | } while (--len);
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| 291 | c = ~c;
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| 292 | return (unsigned long)c;
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| 293 | }
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| 294 |
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| 295 | /* ========================================================================= */
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| 296 | #define DOBIG4 c ^= *++buf4; \
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| 297 | c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
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| 298 | crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
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| 299 | #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
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| 300 |
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| 301 | /* ========================================================================= */
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| 302 | local unsigned long crc32_big(crc, buf, len)
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| 303 | unsigned long crc;
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| 304 | const unsigned char FAR *buf;
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| 305 | unsigned len;
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| 306 | {
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| 307 | register u4 c;
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| 308 | register const u4 FAR *buf4;
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| 309 |
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| 310 | c = REV((u4)crc);
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| 311 | c = ~c;
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| 312 | while (len && ((ptrdiff_t)buf & 3)) {
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| 313 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
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| 314 | len--;
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| 315 | }
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| 316 |
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| 317 | buf4 = (const u4 FAR *)(const void FAR *)buf;
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| 318 | buf4--;
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| 319 | while (len >= 32) {
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| 320 | DOBIG32;
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| 321 | len -= 32;
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| 322 | }
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| 323 | while (len >= 4) {
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| 324 | DOBIG4;
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| 325 | len -= 4;
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| 326 | }
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| 327 | buf4++;
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| 328 | buf = (const unsigned char FAR *)buf4;
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| 329 |
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| 330 | if (len) do {
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| 331 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
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| 332 | } while (--len);
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| 333 | c = ~c;
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| 334 | return (unsigned long)(REV(c));
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| 335 | }
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| 336 |
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| 337 | #endif /* BYFOUR */
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| 338 |
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| 339 | #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
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| 340 |
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| 341 | /* ========================================================================= */
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| 342 | local unsigned long gf2_matrix_times(mat, vec)
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| 343 | unsigned long *mat;
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| 344 | unsigned long vec;
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| 345 | {
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| 346 | unsigned long sum;
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| 347 |
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| 348 | sum = 0;
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| 349 | while (vec) {
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| 350 | if (vec & 1)
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| 351 | sum ^= *mat;
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| 352 | vec >>= 1;
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| 353 | mat++;
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| 354 | }
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| 355 | return sum;
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| 356 | }
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| 357 |
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| 358 | /* ========================================================================= */
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| 359 | local void gf2_matrix_square(square, mat)
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| 360 | unsigned long *square;
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| 361 | unsigned long *mat;
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| 362 | {
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| 363 | int n;
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| 364 |
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| 365 | for (n = 0; n < GF2_DIM; n++)
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| 366 | square[n] = gf2_matrix_times(mat, mat[n]);
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| 367 | }
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| 368 |
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| 369 | /* ========================================================================= */
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| 370 | uLong ZEXPORT crc32_combine(crc1, crc2, len2)
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| 371 | uLong crc1;
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| 372 | uLong crc2;
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| 373 | z_off_t len2;
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| 374 | {
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| 375 | int n;
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| 376 | unsigned long row;
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| 377 | unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
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| 378 | unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
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| 379 |
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| 380 | /* degenerate case */
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| 381 | if (len2 == 0)
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| 382 | return crc1;
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| 383 |
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| 384 | /* put operator for one zero bit in odd */
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| 385 | odd[0] = 0xedb88320L; /* CRC-32 polynomial */
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| 386 | row = 1;
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| 387 | for (n = 1; n < GF2_DIM; n++) {
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| 388 | odd[n] = row;
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| 389 | row <<= 1;
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| 390 | }
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| 391 |
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| 392 | /* put operator for two zero bits in even */
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| 393 | gf2_matrix_square(even, odd);
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| 394 |
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| 395 | /* put operator for four zero bits in odd */
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| 396 | gf2_matrix_square(odd, even);
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| 397 |
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| 398 | /* apply len2 zeros to crc1 (first square will put the operator for one
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| 399 | zero byte, eight zero bits, in even) */
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| 400 | do {
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| 401 | /* apply zeros operator for this bit of len2 */
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| 402 | gf2_matrix_square(even, odd);
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| 403 | if (len2 & 1)
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| 404 | crc1 = gf2_matrix_times(even, crc1);
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| 405 | len2 >>= 1;
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| 406 |
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| 407 | /* if no more bits set, then done */
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| 408 | if (len2 == 0)
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| 409 | break;
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| 410 |
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| 411 | /* another iteration of the loop with odd and even swapped */
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| 412 | gf2_matrix_square(odd, even);
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| 413 | if (len2 & 1)
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| 414 | crc1 = gf2_matrix_times(odd, crc1);
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| 415 | len2 >>= 1;
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| 416 |
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| 417 | /* if no more bits set, then done */
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|---|
| 418 | } while (len2 != 0);
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|---|
| 419 |
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|---|
| 420 | /* return combined crc */
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|---|
| 421 | crc1 ^= crc2;
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| 422 | return crc1;
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|---|
| 423 | }
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