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/* crc32.c -- compute the CRC-32 of a data stream
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* Copyright (C) 1995-2006, 2010 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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* Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
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* CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
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* tables for updating the shift register in one step with three exclusive-ors
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* instead of four steps with four exclusive-ors. This results in about a
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* factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
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Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
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protection on the static variables used to control the first-use generation
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of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
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first call get_crc_table() to initialize the tables before allowing more than
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one thread to use crc32().
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# ifndef DYNAMIC_CRC_TABLE
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# define DYNAMIC_CRC_TABLE
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# endif /* !DYNAMIC_CRC_TABLE */
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#include "zutil.h" /* for STDC and FAR definitions */
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/* Find a four-byte integer type for crc32_little() and crc32_big(). */
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# ifdef STDC /* need ANSI C limits.h to determine sizes */
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# if (UINT_MAX == 0xffffffffUL)
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typedef unsigned int u4;
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# if (ULONG_MAX == 0xffffffffUL)
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typedef unsigned long u4;
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# if (USHRT_MAX == 0xffffffffUL)
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typedef unsigned short u4;
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# undef BYFOUR /* can't find a four-byte integer type! */
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#endif /* !NOBYFOUR */
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/* Definitions for doing the crc four data bytes at a time. */
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# define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
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(((w)&0xff00)<<8)+(((w)&0xff)<<24))
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local unsigned long crc32_little OF((unsigned long,
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const unsigned char FAR *, unsigned));
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local unsigned long crc32_big OF((unsigned long,
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const unsigned char FAR *, unsigned));
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/* Local functions for crc concatenation */
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local unsigned long gf2_matrix_times OF((unsigned long *mat,
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local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
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local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2);
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#ifdef DYNAMIC_CRC_TABLE
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local volatile int crc_table_empty = 1;
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local unsigned long FAR crc_table[TBLS][256];
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local void make_crc_table OF((void));
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local void write_table OF((FILE *, const unsigned long FAR *));
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Generate tables 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 first table is simply the CRC of all possible eight bit values. This is
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all the information needed to generate CRCs on data a byte at a time for all
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combinations of CRC register values and incoming bytes. The remaining tables
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allow for word-at-a-time CRC calculation for both big-endian and little-
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endian machines, where a word is four bytes.
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local void make_crc_table()
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unsigned long poly; /* polynomial exclusive-or pattern */
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/* terms of polynomial defining this crc (except x^32): */
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static volatile int first = 1; /* flag to limit concurrent making */
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static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
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/* See if another task is already doing this (not thread-safe, but better
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than nothing -- significantly reduces duration of vulnerability in
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case the advice about DYNAMIC_CRC_TABLE is ignored) */
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/* make exclusive-or pattern from polynomial (0xedb88320UL) */
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for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
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poly |= 1UL << (31 - p[n]);
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/* generate a crc for every 8-bit value */
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for (n = 0; n < 256; n++) {
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c = (unsigned long)n;
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for (k = 0; k < 8; k++)
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c = c & 1 ? poly ^ (c >> 1) : c >> 1;
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/* generate crc for each value followed by one, two, and three zeros,
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and then the byte reversal of those as well as the first table */
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for (n = 0; n < 256; n++) {
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crc_table[4][n] = REV(c);
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for (k = 1; k < 4; k++) {
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c = crc_table[0][c & 0xff] ^ (c >> 8);
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crc_table[k + 4][n] = REV(c);
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else { /* not first */
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/* wait for the other guy to finish (not efficient, but rare) */
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while (crc_table_empty)
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/* write out CRC tables to crc32.h */
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out = fopen("crc32.h", "w");
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if (out == NULL) return;
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fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
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fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
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fprintf(out, "local const unsigned long FAR ");
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fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
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write_table(out, crc_table[0]);
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fprintf(out, "#ifdef BYFOUR\n");
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for (k = 1; k < 8; k++) {
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fprintf(out, " },\n {\n");
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write_table(out, crc_table[k]);
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fprintf(out, "#endif\n");
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fprintf(out, " }\n};\n");
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#endif /* MAKECRCH */
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local void write_table(out, table)
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const unsigned long FAR *table;
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for (n = 0; n < 256; n++)
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fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
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n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
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#endif /* MAKECRCH */
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#else /* !DYNAMIC_CRC_TABLE */
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/* ========================================================================
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* Tables of CRC-32s of all single-byte values, made by make_crc_table().
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#endif /* DYNAMIC_CRC_TABLE */
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/* =========================================================================
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* This function can be used by asm versions of crc32()
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const unsigned long FAR * ZEXPORT get_crc_table()
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#ifdef DYNAMIC_CRC_TABLE
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#endif /* DYNAMIC_CRC_TABLE */
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return (const unsigned long FAR *)crc_table;
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/* ========================================================================= */
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#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
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#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
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/* ========================================================================= */
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unsigned long ZEXPORT crc32(crc, buf, len)
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const unsigned char FAR *buf;
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if (buf == Z_NULL) return 0UL;
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#ifdef DYNAMIC_CRC_TABLE
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#endif /* DYNAMIC_CRC_TABLE */
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if (sizeof(void *) == sizeof(ptrdiff_t)) {
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if (*((unsigned char *)(&endian)))
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return crc32_little(crc, buf, len);
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return crc32_big(crc, buf, len);
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crc = crc ^ 0xffffffffUL;
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return crc ^ 0xffffffffUL;
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/* ========================================================================= */
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#define DOLIT4 c ^= *buf4++; \
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c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
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crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
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#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
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/* ========================================================================= */
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local unsigned long crc32_little(crc, buf, len)
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const unsigned char FAR *buf;
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register const u4 FAR *buf4;
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while (len && ((ptrdiff_t)buf & 3)) {
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c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
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buf4 = (const u4 FAR *)(const void FAR *)buf;
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buf = (const unsigned char FAR *)buf4;
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c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
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return (unsigned long)c;
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/* ========================================================================= */
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#define DOBIG4 c ^= *++buf4; \
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c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
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crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
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#define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
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/* ========================================================================= */
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local unsigned long crc32_big(crc, buf, len)
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const unsigned char FAR *buf;
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register const u4 FAR *buf4;
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while (len && ((ptrdiff_t)buf & 3)) {
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c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
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buf4 = (const u4 FAR *)(const void FAR *)buf;
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buf = (const unsigned char FAR *)buf4;
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c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
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return (unsigned long)(REV(c));
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#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
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/* ========================================================================= */
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local unsigned long gf2_matrix_times(mat, vec)
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/* ========================================================================= */
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local void gf2_matrix_square(square, mat)
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unsigned long *square;
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for (n = 0; n < GF2_DIM; n++)
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square[n] = gf2_matrix_times(mat, mat[n]);
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/* ========================================================================= */
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local uLong crc32_combine_(crc1, crc2, len2)
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unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
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unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
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/* degenerate case (also disallow negative lengths) */
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/* put operator for one zero bit in odd */
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odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
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for (n = 1; n < GF2_DIM; n++) {
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/* put operator for two zero bits in even */
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gf2_matrix_square(even, odd);
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/* put operator for four zero bits in odd */
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gf2_matrix_square(odd, even);
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/* apply len2 zeros to crc1 (first square will put the operator for one
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zero byte, eight zero bits, in even) */
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/* apply zeros operator for this bit of len2 */
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gf2_matrix_square(even, odd);
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crc1 = gf2_matrix_times(even, crc1);
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/* if no more bits set, then done */
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/* another iteration of the loop with odd and even swapped */
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gf2_matrix_square(odd, even);
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crc1 = gf2_matrix_times(odd, crc1);
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/* if no more bits set, then done */
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/* return combined crc */
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/* ========================================================================= */
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uLong ZEXPORT crc32_combine(crc1, crc2, len2)
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return crc32_combine_(crc1, crc2, len2);
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uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
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return crc32_combine_(crc1, crc2, len2);
added
removed
zlib/crc32.c
