author  Ryan C. Gordon <icculus@icculus.org> 
Mon, 14 Mar 2005 11:49:30 +0000  
changeset 691  71d9affe0d8a 
parent 602  691c1eadb8b7 
permissions  rwrr 
602
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/* crc32.c  compute the CRC32 of a data stream 
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* Copyright (C) 19952003 Mark Adler 
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* For conditions of distribution and use, see copyright notice in zlib.h 
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* 
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* Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster 
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* CRC methods: exclusiveoring 32 bits of data at a time, and precomputing 
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* tables for updating the shift register in one step with three exclusiveors 
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* instead of four steps with four exclusiveors. This results about a factor 
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* of two increase in speed on a Power PC G4 (PPC7455) using gcc O3. 
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*/ 
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/* @(#) $Id: crc32.c,v 1.1 2003/12/07 05:29:20 icculus Exp $ */ 
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#ifdef MAKECRCH 
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# include <stdio.h> 
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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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#endif /* MAKECRCH */ 
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#include "zutil.h" /* for STDC and FAR definitions */ 
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#define local static 
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/* Find a fourbyte integer type for crc32_little() and crc32_big(). */ 
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#ifndef NOBYFOUR 
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# ifdef STDC /* need ANSI C limits.h to determine sizes */ 
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# include <limits.h> 
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# define BYFOUR 
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# if (UINT_MAX == 0xffffffffUL) 
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typedef unsigned int u4; 
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# else 
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# if (ULONG_MAX == 0xffffffffUL) 
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typedef unsigned long u4; 
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# else 
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# if (USHRT_MAX == 0xffffffffUL) 
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typedef unsigned short u4; 
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# else 
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# undef BYFOUR /* can't find a fourbyte integer type! */ 
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# endif 
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# endif 
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# endif 
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# endif /* STDC */ 
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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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#ifdef BYFOUR 
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# define REV(w) (((w)>>24)+(((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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# define TBLS 8 
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#else 
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# define TBLS 1 
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#endif /* BYFOUR */ 
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#ifdef DYNAMIC_CRC_TABLE 
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local 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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#ifdef MAKECRCH 
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local void write_table OF((FILE *, const unsigned long FAR *)); 
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#endif /* MAKECRCH */ 
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/* 
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Generate tables for a bytewise 32bit 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 exclusiveor, 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 shiftregister 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 wordatatime CRC calculation for both bigendian and little 
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endian machines, where a word is four bytes. 
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*/ 
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local void make_crc_table() 
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{ 
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unsigned long c; 
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int n, k; 
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unsigned long poly; /* polynomial exclusiveor pattern */ 
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/* terms of polynomial defining this crc (except x^32): */ 
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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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/* make exclusiveor pattern from polynomial (0xedb88320UL) */ 
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poly = 0UL; 
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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 8bit 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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crc_table[0][n] = c; 
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} 
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#ifdef BYFOUR 
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/* generate crc for each value followed by one, two, and three zeros, and 
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then the byte reversal of those as well as the first table */ 
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118 
for (n = 0; n < 256; n++) { 
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119 
c = crc_table[0][n]; 
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120 
crc_table[4][n] = REV(c); 
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121 
for (k = 1; k < 4; k++) { 
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122 
c = crc_table[0][c & 0xff] ^ (c >> 8); 
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123 
crc_table[k][n] = c; 
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crc_table[k + 4][n] = REV(c); 
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125 
} 
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126 
} 
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127 
#endif /* BYFOUR */ 
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128 

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crc_table_empty = 0; 
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130 

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#ifdef MAKECRCH 
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132 
/* write out CRC tables to crc32.h */ 
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{ 
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FILE *out; 
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135 

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out = fopen("crc32.h", "w"); 
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137 
if (out == NULL) return; 
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138 
fprintf(out, "/* crc32.h  tables for rapid CRC calculation\n"); 
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139 
fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); 
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140 
fprintf(out, "local const unsigned long FAR "); 
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141 
fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); 
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write_table(out, crc_table[0]); 
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143 
# ifdef BYFOUR 
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fprintf(out, "#ifdef BYFOUR\n"); 
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145 
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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148 
} 
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149 
fprintf(out, "#endif\n"); 
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# endif /* BYFOUR */ 
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fprintf(out, " }\n};\n"); 
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fclose(out); 
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153 
} 
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#endif /* MAKECRCH */ 
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155 
} 
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156 

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#ifdef MAKECRCH 
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158 
local void write_table(out, table) 
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FILE *out; 
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160 
const unsigned long FAR *table; 
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161 
{ 
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162 
int n; 
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163 

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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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166 
n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); 
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167 
} 
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#endif /* MAKECRCH */ 
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169 

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#else /* !DYNAMIC_CRC_TABLE */ 
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/* ======================================================================== 
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* Tables of CRC32s of all singlebyte values, made by make_crc_table(). 
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*/ 
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#include "crc32.h" 
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#endif /* DYNAMIC_CRC_TABLE */ 
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176 

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/* ========================================================================= 
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* This function can be used by asm versions of crc32() 
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179 
*/ 
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const unsigned long FAR * ZEXPORT get_crc_table() 
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181 
{ 
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#ifdef DYNAMIC_CRC_TABLE 
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183 
if (crc_table_empty) make_crc_table(); 
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184 
#endif /* DYNAMIC_CRC_TABLE */ 
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185 
return (const unsigned long FAR *)crc_table; 
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186 
} 
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187 

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/* ========================================================================= */ 
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189 
#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) 
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190 
#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 
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191 

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/* ========================================================================= */ 
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193 
unsigned long ZEXPORT crc32(crc, buf, len) 
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194 
unsigned long crc; 
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195 
const unsigned char FAR *buf; 
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196 
unsigned len; 
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197 
{ 
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198 
if (buf == Z_NULL) return 0UL; 
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199 

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200 
#ifdef DYNAMIC_CRC_TABLE 
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201 
if (crc_table_empty) 
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202 
make_crc_table(); 
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203 
#endif /* DYNAMIC_CRC_TABLE */ 
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204 

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205 
#ifdef BYFOUR 
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206 
if (sizeof(void *) == sizeof(ptrdiff_t)) { 
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207 
u4 endian; 
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208 

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endian = 1; 
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210 
if (*((unsigned char *)(&endian))) 
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211 
return crc32_little(crc, buf, len); 
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212 
else 
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213 
return crc32_big(crc, buf, len); 
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214 
} 
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215 
#endif /* BYFOUR */ 
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216 
crc = crc ^ 0xffffffffUL; 
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217 
while (len >= 8) { 
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218 
DO8; 
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219 
len = 8; 
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220 
} 
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221 
if (len) do { 
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222 
DO1; 
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223 
} while (len); 
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224 
return crc ^ 0xffffffffUL; 
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225 
} 
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226 

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227 
#ifdef BYFOUR 
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228 

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229 
/* ========================================================================= */ 
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230 
#define DOLIT4 c ^= *buf4++; \ 
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231 
c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ 
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232 
crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] 
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233 
#define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 
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234 

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235 
/* ========================================================================= */ 
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236 
local unsigned long crc32_little(crc, buf, len) 
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237 
unsigned long crc; 
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238 
const unsigned char FAR *buf; 
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unsigned len; 
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{ 
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register u4 c; 
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register const u4 FAR *buf4; 
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243 

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c = (u4)crc; 
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c = ~c; 
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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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len; 
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} 
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buf4 = (const u4 FAR *)buf; 
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while (len >= 32) { 
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DOLIT32; 
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len = 32; 
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} 
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while (len >= 4) { 
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DOLIT4; 
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len = 4; 
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} 
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buf = (const unsigned char FAR *)buf4; 
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261 

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if (len) do { 
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c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); 
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} while (len); 
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c = ~c; 
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return (unsigned long)c; 
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} 
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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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unsigned long crc; 
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const unsigned char FAR *buf; 
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unsigned len; 
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{ 
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register u4 c; 
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register const u4 FAR *buf4; 
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c = REV((u4)crc); 
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c = ~c; 
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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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len; 
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} 
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buf4 = (const u4 FAR *)buf; 
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buf4; 
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while (len >= 32) { 
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DOBIG32; 
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len = 32; 
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} 
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while (len >= 4) { 
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DOBIG4; 
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len = 4; 
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} 
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buf4++; 
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buf = (const unsigned char FAR *)buf4; 
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303 

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if (len) do { 
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c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); 
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} while (len); 
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c = ~c; 
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return (unsigned long)(REV(c)); 
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} 
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#endif /* BYFOUR */ 