[562] | 1 | /* crc32.c -- compute the CRC-32 of a data stream |
---|
| 2 | * Copyright (C) 1995-2003 Mark Adler |
---|
| 3 | * For conditions of distribution and use, see copyright notice in zlib.h |
---|
| 4 | * |
---|
| 5 | * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster |
---|
| 6 | * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing |
---|
| 7 | * tables for updating the shift register in one step with three exclusive-ors |
---|
| 8 | * instead of four steps with four exclusive-ors. This results about a factor |
---|
| 9 | * of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3. |
---|
| 10 | */ |
---|
| 11 | |
---|
| 12 | /* @(#) $Id: crc32.cc,v 1.1 2005/05/12 21:04:53 duns Exp $ */ |
---|
| 13 | |
---|
| 14 | /* |
---|
| 15 | Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore |
---|
| 16 | protection on the static variables used to control the first-use generation |
---|
| 17 | of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should |
---|
| 18 | first call get_crc_table() to initialize the tables before allowing more than |
---|
| 19 | one thread to use crc32(). |
---|
| 20 | */ |
---|
| 21 | |
---|
| 22 | #ifdef MAKECRCH |
---|
| 23 | # include <stdio.h> |
---|
| 24 | # ifndef DYNAMIC_CRC_TABLE |
---|
| 25 | # define DYNAMIC_CRC_TABLE |
---|
| 26 | # endif /* !DYNAMIC_CRC_TABLE */ |
---|
| 27 | #endif /* MAKECRCH */ |
---|
| 28 | |
---|
| 29 | #include "zutil.h" /* for STDC and FAR definitions */ |
---|
| 30 | |
---|
| 31 | #define local static |
---|
| 32 | |
---|
| 33 | /* Find a four-byte integer type for crc32_little() and crc32_big(). */ |
---|
| 34 | #ifndef NOBYFOUR |
---|
| 35 | # ifdef STDC /* need ANSI C limits.h to determine sizes */ |
---|
| 36 | # include <limits.h> |
---|
| 37 | # define BYFOUR |
---|
| 38 | # if (UINT_MAX == 0xffffffffUL) |
---|
| 39 | typedef unsigned int u4; |
---|
| 40 | # else |
---|
| 41 | # if (ULONG_MAX == 0xffffffffUL) |
---|
| 42 | typedef unsigned long u4; |
---|
| 43 | # else |
---|
| 44 | # if (USHRT_MAX == 0xffffffffUL) |
---|
| 45 | typedef unsigned short u4; |
---|
| 46 | # else |
---|
| 47 | # undef BYFOUR /* can't find a four-byte integer type! */ |
---|
| 48 | # endif |
---|
| 49 | # endif |
---|
| 50 | # endif |
---|
| 51 | # endif /* STDC */ |
---|
| 52 | #endif /* !NOBYFOUR */ |
---|
| 53 | |
---|
| 54 | /* Definitions for doing the crc four data bytes at a time. */ |
---|
| 55 | #ifdef BYFOUR |
---|
| 56 | # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \ |
---|
| 57 | (((w)&0xff00)<<8)+(((w)&0xff)<<24)) |
---|
| 58 | local unsigned long crc32_little OF((unsigned long, |
---|
| 59 | const unsigned char FAR *, unsigned)); |
---|
| 60 | local unsigned long crc32_big OF((unsigned long, |
---|
| 61 | const unsigned char FAR *, unsigned)); |
---|
| 62 | # define TBLS 8 |
---|
| 63 | #else |
---|
| 64 | # define TBLS 1 |
---|
| 65 | #endif /* BYFOUR */ |
---|
| 66 | |
---|
| 67 | #ifdef DYNAMIC_CRC_TABLE |
---|
| 68 | |
---|
| 69 | local volatile int crc_table_empty = 1; |
---|
| 70 | local unsigned long FAR crc_table[TBLS][256]; |
---|
| 71 | local void make_crc_table OF((void)); |
---|
| 72 | #ifdef MAKECRCH |
---|
| 73 | local void write_table OF((FILE *, const unsigned long FAR *)); |
---|
| 74 | #endif /* MAKECRCH */ |
---|
| 75 | |
---|
| 76 | /* |
---|
| 77 | Generate tables for a byte-wise 32-bit CRC calculation on the polynomial: |
---|
| 78 | 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. |
---|
| 79 | |
---|
| 80 | Polynomials over GF(2) are represented in binary, one bit per coefficient, |
---|
| 81 | with the lowest powers in the most significant bit. Then adding polynomials |
---|
| 82 | is just exclusive-or, and multiplying a polynomial by x is a right shift by |
---|
| 83 | one. If we call the above polynomial p, and represent a byte as the |
---|
| 84 | polynomial q, also with the lowest power in the most significant bit (so the |
---|
| 85 | byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p, |
---|
| 86 | where a mod b means the remainder after dividing a by b. |
---|
| 87 | |
---|
| 88 | This calculation is done using the shift-register method of multiplying and |
---|
| 89 | taking the remainder. The register is initialized to zero, and for each |
---|
| 90 | incoming bit, x^32 is added mod p to the register if the bit is a one (where |
---|
| 91 | x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by |
---|
| 92 | x (which is shifting right by one and adding x^32 mod p if the bit shifted |
---|
| 93 | out is a one). We start with the highest power (least significant bit) of |
---|
| 94 | q and repeat for all eight bits of q. |
---|
| 95 | |
---|
| 96 | The first table is simply the CRC of all possible eight bit values. This is |
---|
| 97 | all the information needed to generate CRCs on data a byte at a time for all |
---|
| 98 | combinations of CRC register values and incoming bytes. The remaining tables |
---|
| 99 | allow for word-at-a-time CRC calculation for both big-endian and little- |
---|
| 100 | endian machines, where a word is four bytes. |
---|
| 101 | */ |
---|
| 102 | local void make_crc_table() |
---|
| 103 | { |
---|
| 104 | unsigned long c; |
---|
| 105 | int n, k; |
---|
| 106 | unsigned long poly; /* polynomial exclusive-or pattern */ |
---|
| 107 | /* terms of polynomial defining this crc (except x^32): */ |
---|
| 108 | static volatile int first = 1; /* flag to limit concurrent making */ |
---|
| 109 | static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26}; |
---|
| 110 | |
---|
| 111 | /* See if another task is already doing this (not thread-safe, but better |
---|
| 112 | than nothing -- significantly reduces duration of vulnerability in |
---|
| 113 | case the advice about DYNAMIC_CRC_TABLE is ignored) */ |
---|
| 114 | if (first) { |
---|
| 115 | first = 0; |
---|
| 116 | |
---|
| 117 | /* make exclusive-or pattern from polynomial (0xedb88320UL) */ |
---|
| 118 | poly = 0UL; |
---|
| 119 | for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++) |
---|
| 120 | poly |= 1UL << (31 - p[n]); |
---|
| 121 | |
---|
| 122 | /* generate a crc for every 8-bit value */ |
---|
| 123 | for (n = 0; n < 256; n++) { |
---|
| 124 | c = (unsigned long)n; |
---|
| 125 | for (k = 0; k < 8; k++) |
---|
| 126 | c = c & 1 ? poly ^ (c >> 1) : c >> 1; |
---|
| 127 | crc_table[0][n] = c; |
---|
| 128 | } |
---|
| 129 | |
---|
| 130 | #ifdef BYFOUR |
---|
| 131 | /* generate crc for each value followed by one, two, and three zeros, |
---|
| 132 | and then the byte reversal of those as well as the first table */ |
---|
| 133 | for (n = 0; n < 256; n++) { |
---|
| 134 | c = crc_table[0][n]; |
---|
| 135 | crc_table[4][n] = REV(c); |
---|
| 136 | for (k = 1; k < 4; k++) { |
---|
| 137 | c = crc_table[0][c & 0xff] ^ (c >> 8); |
---|
| 138 | crc_table[k][n] = c; |
---|
| 139 | crc_table[k + 4][n] = REV(c); |
---|
| 140 | } |
---|
| 141 | } |
---|
| 142 | #endif /* BYFOUR */ |
---|
| 143 | |
---|
| 144 | crc_table_empty = 0; |
---|
| 145 | } |
---|
| 146 | else { /* not first */ |
---|
| 147 | /* wait for the other guy to finish (not efficient, but rare) */ |
---|
| 148 | while (crc_table_empty) |
---|
| 149 | ; |
---|
| 150 | } |
---|
| 151 | |
---|
| 152 | #ifdef MAKECRCH |
---|
| 153 | /* write out CRC tables to crc32.h */ |
---|
| 154 | { |
---|
| 155 | FILE *out; |
---|
| 156 | |
---|
| 157 | out = fopen("crc32.h", "w"); |
---|
| 158 | if (out == NULL) return; |
---|
| 159 | fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n"); |
---|
| 160 | fprintf(out, " * Generated automatically by crc32.c\n */\n\n"); |
---|
| 161 | fprintf(out, "local const unsigned long FAR "); |
---|
| 162 | fprintf(out, "crc_table[TBLS][256] =\n{\n {\n"); |
---|
| 163 | write_table(out, crc_table[0]); |
---|
| 164 | # ifdef BYFOUR |
---|
| 165 | fprintf(out, "#ifdef BYFOUR\n"); |
---|
| 166 | for (k = 1; k < 8; k++) { |
---|
| 167 | fprintf(out, " },\n {\n"); |
---|
| 168 | write_table(out, crc_table[k]); |
---|
| 169 | } |
---|
| 170 | fprintf(out, "#endif\n"); |
---|
| 171 | # endif /* BYFOUR */ |
---|
| 172 | fprintf(out, " }\n};\n"); |
---|
| 173 | fclose(out); |
---|
| 174 | } |
---|
| 175 | #endif /* MAKECRCH */ |
---|
| 176 | } |
---|
| 177 | |
---|
| 178 | #ifdef MAKECRCH |
---|
| 179 | local void write_table(FILE *out, const unsigned long FAR *table) |
---|
| 180 | { |
---|
| 181 | int n; |
---|
| 182 | |
---|
| 183 | for (n = 0; n < 256; n++) |
---|
| 184 | fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n], |
---|
| 185 | n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", ")); |
---|
| 186 | } |
---|
| 187 | #endif /* MAKECRCH */ |
---|
| 188 | |
---|
| 189 | #else /* !DYNAMIC_CRC_TABLE */ |
---|
| 190 | /* ======================================================================== |
---|
| 191 | * Tables of CRC-32s of all single-byte values, made by make_crc_table(). |
---|
| 192 | */ |
---|
| 193 | #include "crc32.h" |
---|
| 194 | #endif /* DYNAMIC_CRC_TABLE */ |
---|
| 195 | |
---|
| 196 | /* ========================================================================= |
---|
| 197 | * This function can be used by asm versions of crc32() |
---|
| 198 | */ |
---|
| 199 | const unsigned long FAR * ZEXPORT get_crc_table() |
---|
| 200 | { |
---|
| 201 | #ifdef DYNAMIC_CRC_TABLE |
---|
| 202 | if (crc_table_empty) |
---|
| 203 | make_crc_table(); |
---|
| 204 | #endif /* DYNAMIC_CRC_TABLE */ |
---|
| 205 | return (const unsigned long FAR *)crc_table; |
---|
| 206 | } |
---|
| 207 | |
---|
| 208 | /* ========================================================================= */ |
---|
| 209 | #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8) |
---|
| 210 | #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1 |
---|
| 211 | |
---|
| 212 | /* ========================================================================= */ |
---|
| 213 | unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
---|
| 214 | { |
---|
| 215 | if (buf == Z_NULL) return 0UL; |
---|
| 216 | |
---|
| 217 | #ifdef DYNAMIC_CRC_TABLE |
---|
| 218 | if (crc_table_empty) |
---|
| 219 | make_crc_table(); |
---|
| 220 | #endif /* DYNAMIC_CRC_TABLE */ |
---|
| 221 | |
---|
| 222 | #ifdef BYFOUR |
---|
| 223 | if (sizeof(void *) == sizeof(ptrdiff_t)) { |
---|
| 224 | u4 endian; |
---|
| 225 | |
---|
| 226 | endian = 1; |
---|
| 227 | if (*((unsigned char *)(&endian))) |
---|
| 228 | return crc32_little(crc, buf, len); |
---|
| 229 | else |
---|
| 230 | return crc32_big(crc, buf, len); |
---|
| 231 | } |
---|
| 232 | #endif /* BYFOUR */ |
---|
| 233 | crc = crc ^ 0xffffffffUL; |
---|
| 234 | while (len >= 8) { |
---|
| 235 | DO8; |
---|
| 236 | len -= 8; |
---|
| 237 | } |
---|
| 238 | if (len) do { |
---|
| 239 | DO1; |
---|
| 240 | } while (--len); |
---|
| 241 | return crc ^ 0xffffffffUL; |
---|
| 242 | } |
---|
| 243 | |
---|
| 244 | #ifdef BYFOUR |
---|
| 245 | |
---|
| 246 | /* ========================================================================= */ |
---|
| 247 | #define DOLIT4 c ^= *buf4++; \ |
---|
| 248 | c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \ |
---|
| 249 | crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24] |
---|
| 250 | #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4 |
---|
| 251 | |
---|
| 252 | /* ========================================================================= */ |
---|
| 253 | local unsigned long crc32_little(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
---|
| 254 | { |
---|
| 255 | register u4 c; |
---|
| 256 | register const u4 FAR *buf4; |
---|
| 257 | |
---|
| 258 | c = (u4)crc; |
---|
| 259 | c = ~c; |
---|
| 260 | while (len && ((ptrdiff_t)buf & 3)) { |
---|
| 261 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
---|
| 262 | len--; |
---|
| 263 | } |
---|
| 264 | |
---|
| 265 | buf4 = (const u4 FAR *)buf; |
---|
| 266 | while (len >= 32) { |
---|
| 267 | DOLIT32; |
---|
| 268 | len -= 32; |
---|
| 269 | } |
---|
| 270 | while (len >= 4) { |
---|
| 271 | DOLIT4; |
---|
| 272 | len -= 4; |
---|
| 273 | } |
---|
| 274 | buf = (const unsigned char FAR *)buf4; |
---|
| 275 | |
---|
| 276 | if (len) do { |
---|
| 277 | c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8); |
---|
| 278 | } while (--len); |
---|
| 279 | c = ~c; |
---|
| 280 | return (unsigned long)c; |
---|
| 281 | } |
---|
| 282 | |
---|
| 283 | /* ========================================================================= */ |
---|
| 284 | #define DOBIG4 c ^= *++buf4; \ |
---|
| 285 | c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \ |
---|
| 286 | crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24] |
---|
| 287 | #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4 |
---|
| 288 | |
---|
| 289 | /* ========================================================================= */ |
---|
| 290 | local unsigned long crc32_big(unsigned long crc, const unsigned char FAR *buf, unsigned len) |
---|
| 291 | { |
---|
| 292 | register u4 c; |
---|
| 293 | register const u4 FAR *buf4; |
---|
| 294 | |
---|
| 295 | c = REV((u4)crc); |
---|
| 296 | c = ~c; |
---|
| 297 | while (len && ((ptrdiff_t)buf & 3)) { |
---|
| 298 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
---|
| 299 | len--; |
---|
| 300 | } |
---|
| 301 | |
---|
| 302 | buf4 = (const u4 FAR *)buf; |
---|
| 303 | buf4--; |
---|
| 304 | while (len >= 32) { |
---|
| 305 | DOBIG32; |
---|
| 306 | len -= 32; |
---|
| 307 | } |
---|
| 308 | while (len >= 4) { |
---|
| 309 | DOBIG4; |
---|
| 310 | len -= 4; |
---|
| 311 | } |
---|
| 312 | buf4++; |
---|
| 313 | buf = (const unsigned char FAR *)buf4; |
---|
| 314 | |
---|
| 315 | if (len) do { |
---|
| 316 | c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8); |
---|
| 317 | } while (--len); |
---|
| 318 | c = ~c; |
---|
| 319 | return (unsigned long)(REV(c)); |
---|
| 320 | } |
---|
| 321 | |
---|
| 322 | #endif /* BYFOUR */ |
---|