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annotate libs/zlib/crc32.c @ 43:73813c1176de

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author John Tsiombikas <nuclear@member.fsf.org>
date Fri, 14 Aug 2015 04:33:42 +0300
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nuclear@26 1 /* crc32.c -- compute the CRC-32 of a data stream
nuclear@26 2 * Copyright (C) 1995-2005 Mark Adler
nuclear@26 3 * For conditions of distribution and use, see copyright notice in zlib.h
nuclear@26 4 *
nuclear@26 5 * Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
nuclear@26 6 * CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
nuclear@26 7 * tables for updating the shift register in one step with three exclusive-ors
nuclear@26 8 * instead of four steps with four exclusive-ors. This results in about a
nuclear@26 9 * factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
nuclear@26 10 */
nuclear@26 11
nuclear@26 12 /* @(#) $Id$ */
nuclear@26 13
nuclear@26 14 /*
nuclear@26 15 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
nuclear@26 16 protection on the static variables used to control the first-use generation
nuclear@26 17 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
nuclear@26 18 first call get_crc_table() to initialize the tables before allowing more than
nuclear@26 19 one thread to use crc32().
nuclear@26 20 */
nuclear@26 21
nuclear@26 22 #ifdef MAKECRCH
nuclear@26 23 # include <stdio.h>
nuclear@26 24 # ifndef DYNAMIC_CRC_TABLE
nuclear@26 25 # define DYNAMIC_CRC_TABLE
nuclear@26 26 # endif /* !DYNAMIC_CRC_TABLE */
nuclear@26 27 #endif /* MAKECRCH */
nuclear@26 28
nuclear@26 29 #include "zutil.h" /* for STDC and FAR definitions */
nuclear@26 30
nuclear@26 31 #define local static
nuclear@26 32
nuclear@26 33 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
nuclear@26 34 #ifndef NOBYFOUR
nuclear@26 35 # ifdef STDC /* need ANSI C limits.h to determine sizes */
nuclear@26 36 # include <limits.h>
nuclear@26 37 # define BYFOUR
nuclear@26 38 # if (UINT_MAX == 0xffffffffUL)
nuclear@26 39 typedef unsigned int u4;
nuclear@26 40 # else
nuclear@26 41 # if (ULONG_MAX == 0xffffffffUL)
nuclear@26 42 typedef unsigned long u4;
nuclear@26 43 # else
nuclear@26 44 # if (USHRT_MAX == 0xffffffffUL)
nuclear@26 45 typedef unsigned short u4;
nuclear@26 46 # else
nuclear@26 47 # undef BYFOUR /* can't find a four-byte integer type! */
nuclear@26 48 # endif
nuclear@26 49 # endif
nuclear@26 50 # endif
nuclear@26 51 # endif /* STDC */
nuclear@26 52 #endif /* !NOBYFOUR */
nuclear@26 53
nuclear@26 54 /* Definitions for doing the crc four data bytes at a time. */
nuclear@26 55 #ifdef BYFOUR
nuclear@26 56 # define REV(w) (((w)>>24)+(((w)>>8)&0xff00)+ \
nuclear@26 57 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
nuclear@26 58 local unsigned long crc32_little OF((unsigned long,
nuclear@26 59 const unsigned char FAR *, unsigned));
nuclear@26 60 local unsigned long crc32_big OF((unsigned long,
nuclear@26 61 const unsigned char FAR *, unsigned));
nuclear@26 62 # define TBLS 8
nuclear@26 63 #else
nuclear@26 64 # define TBLS 1
nuclear@26 65 #endif /* BYFOUR */
nuclear@26 66
nuclear@26 67 /* Local functions for crc concatenation */
nuclear@26 68 local unsigned long gf2_matrix_times OF((unsigned long *mat,
nuclear@26 69 unsigned long vec));
nuclear@26 70 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
nuclear@26 71
nuclear@26 72 #ifdef DYNAMIC_CRC_TABLE
nuclear@26 73
nuclear@26 74 local volatile int crc_table_empty = 1;
nuclear@26 75 local unsigned long FAR crc_table[TBLS][256];
nuclear@26 76 local void make_crc_table OF((void));
nuclear@26 77 #ifdef MAKECRCH
nuclear@26 78 local void write_table OF((FILE *, const unsigned long FAR *));
nuclear@26 79 #endif /* MAKECRCH */
nuclear@26 80 /*
nuclear@26 81 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
nuclear@26 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.
nuclear@26 83
nuclear@26 84 Polynomials over GF(2) are represented in binary, one bit per coefficient,
nuclear@26 85 with the lowest powers in the most significant bit. Then adding polynomials
nuclear@26 86 is just exclusive-or, and multiplying a polynomial by x is a right shift by
nuclear@26 87 one. If we call the above polynomial p, and represent a byte as the
nuclear@26 88 polynomial q, also with the lowest power in the most significant bit (so the
nuclear@26 89 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
nuclear@26 90 where a mod b means the remainder after dividing a by b.
nuclear@26 91
nuclear@26 92 This calculation is done using the shift-register method of multiplying and
nuclear@26 93 taking the remainder. The register is initialized to zero, and for each
nuclear@26 94 incoming bit, x^32 is added mod p to the register if the bit is a one (where
nuclear@26 95 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
nuclear@26 96 x (which is shifting right by one and adding x^32 mod p if the bit shifted
nuclear@26 97 out is a one). We start with the highest power (least significant bit) of
nuclear@26 98 q and repeat for all eight bits of q.
nuclear@26 99
nuclear@26 100 The first table is simply the CRC of all possible eight bit values. This is
nuclear@26 101 all the information needed to generate CRCs on data a byte at a time for all
nuclear@26 102 combinations of CRC register values and incoming bytes. The remaining tables
nuclear@26 103 allow for word-at-a-time CRC calculation for both big-endian and little-
nuclear@26 104 endian machines, where a word is four bytes.
nuclear@26 105 */
nuclear@26 106 local void make_crc_table()
nuclear@26 107 {
nuclear@26 108 unsigned long c;
nuclear@26 109 int n, k;
nuclear@26 110 unsigned long poly; /* polynomial exclusive-or pattern */
nuclear@26 111 /* terms of polynomial defining this crc (except x^32): */
nuclear@26 112 static volatile int first = 1; /* flag to limit concurrent making */
nuclear@26 113 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
nuclear@26 114
nuclear@26 115 /* See if another task is already doing this (not thread-safe, but better
nuclear@26 116 than nothing -- significantly reduces duration of vulnerability in
nuclear@26 117 case the advice about DYNAMIC_CRC_TABLE is ignored) */
nuclear@26 118 if (first) {
nuclear@26 119 first = 0;
nuclear@26 120
nuclear@26 121 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
nuclear@26 122 poly = 0UL;
nuclear@26 123 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
nuclear@26 124 poly |= 1UL << (31 - p[n]);
nuclear@26 125
nuclear@26 126 /* generate a crc for every 8-bit value */
nuclear@26 127 for (n = 0; n < 256; n++) {
nuclear@26 128 c = (unsigned long)n;
nuclear@26 129 for (k = 0; k < 8; k++)
nuclear@26 130 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
nuclear@26 131 crc_table[0][n] = c;
nuclear@26 132 }
nuclear@26 133
nuclear@26 134 #ifdef BYFOUR
nuclear@26 135 /* generate crc for each value followed by one, two, and three zeros,
nuclear@26 136 and then the byte reversal of those as well as the first table */
nuclear@26 137 for (n = 0; n < 256; n++) {
nuclear@26 138 c = crc_table[0][n];
nuclear@26 139 crc_table[4][n] = REV(c);
nuclear@26 140 for (k = 1; k < 4; k++) {
nuclear@26 141 c = crc_table[0][c & 0xff] ^ (c >> 8);
nuclear@26 142 crc_table[k][n] = c;
nuclear@26 143 crc_table[k + 4][n] = REV(c);
nuclear@26 144 }
nuclear@26 145 }
nuclear@26 146 #endif /* BYFOUR */
nuclear@26 147
nuclear@26 148 crc_table_empty = 0;
nuclear@26 149 }
nuclear@26 150 else { /* not first */
nuclear@26 151 /* wait for the other guy to finish (not efficient, but rare) */
nuclear@26 152 while (crc_table_empty)
nuclear@26 153 ;
nuclear@26 154 }
nuclear@26 155
nuclear@26 156 #ifdef MAKECRCH
nuclear@26 157 /* write out CRC tables to crc32.h */
nuclear@26 158 {
nuclear@26 159 FILE *out;
nuclear@26 160
nuclear@26 161 out = fopen("crc32.h", "w");
nuclear@26 162 if (out == NULL) return;
nuclear@26 163 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
nuclear@26 164 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
nuclear@26 165 fprintf(out, "local const unsigned long FAR ");
nuclear@26 166 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
nuclear@26 167 write_table(out, crc_table[0]);
nuclear@26 168 # ifdef BYFOUR
nuclear@26 169 fprintf(out, "#ifdef BYFOUR\n");
nuclear@26 170 for (k = 1; k < 8; k++) {
nuclear@26 171 fprintf(out, " },\n {\n");
nuclear@26 172 write_table(out, crc_table[k]);
nuclear@26 173 }
nuclear@26 174 fprintf(out, "#endif\n");
nuclear@26 175 # endif /* BYFOUR */
nuclear@26 176 fprintf(out, " }\n};\n");
nuclear@26 177 fclose(out);
nuclear@26 178 }
nuclear@26 179 #endif /* MAKECRCH */
nuclear@26 180 }
nuclear@26 181
nuclear@26 182 #ifdef MAKECRCH
nuclear@26 183 local void write_table(out, table)
nuclear@26 184 FILE *out;
nuclear@26 185 const unsigned long FAR *table;
nuclear@26 186 {
nuclear@26 187 int n;
nuclear@26 188
nuclear@26 189 for (n = 0; n < 256; n++)
nuclear@26 190 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
nuclear@26 191 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
nuclear@26 192 }
nuclear@26 193 #endif /* MAKECRCH */
nuclear@26 194
nuclear@26 195 #else /* !DYNAMIC_CRC_TABLE */
nuclear@26 196 /* ========================================================================
nuclear@26 197 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
nuclear@26 198 */
nuclear@26 199 #include "crc32.h"
nuclear@26 200 #endif /* DYNAMIC_CRC_TABLE */
nuclear@26 201
nuclear@26 202 /* =========================================================================
nuclear@26 203 * This function can be used by asm versions of crc32()
nuclear@26 204 */
nuclear@26 205 const unsigned long FAR * ZEXPORT get_crc_table()
nuclear@26 206 {
nuclear@26 207 #ifdef DYNAMIC_CRC_TABLE
nuclear@26 208 if (crc_table_empty)
nuclear@26 209 make_crc_table();
nuclear@26 210 #endif /* DYNAMIC_CRC_TABLE */
nuclear@26 211 return (const unsigned long FAR *)crc_table;
nuclear@26 212 }
nuclear@26 213
nuclear@26 214 /* ========================================================================= */
nuclear@26 215 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
nuclear@26 216 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
nuclear@26 217
nuclear@26 218 /* ========================================================================= */
nuclear@26 219 unsigned long ZEXPORT crc32(crc, buf, len)
nuclear@26 220 unsigned long crc;
nuclear@26 221 const unsigned char FAR *buf;
nuclear@26 222 unsigned len;
nuclear@26 223 {
nuclear@26 224 if (buf == Z_NULL) return 0UL;
nuclear@26 225
nuclear@26 226 #ifdef DYNAMIC_CRC_TABLE
nuclear@26 227 if (crc_table_empty)
nuclear@26 228 make_crc_table();
nuclear@26 229 #endif /* DYNAMIC_CRC_TABLE */
nuclear@26 230
nuclear@26 231 #ifdef BYFOUR
nuclear@26 232 if (sizeof(void *) == sizeof(ptrdiff_t)) {
nuclear@26 233 u4 endian;
nuclear@26 234
nuclear@26 235 endian = 1;
nuclear@26 236 if (*((unsigned char *)(&endian)))
nuclear@26 237 return crc32_little(crc, buf, len);
nuclear@26 238 else
nuclear@26 239 return crc32_big(crc, buf, len);
nuclear@26 240 }
nuclear@26 241 #endif /* BYFOUR */
nuclear@26 242 crc = crc ^ 0xffffffffUL;
nuclear@26 243 while (len >= 8) {
nuclear@26 244 DO8;
nuclear@26 245 len -= 8;
nuclear@26 246 }
nuclear@26 247 if (len) do {
nuclear@26 248 DO1;
nuclear@26 249 } while (--len);
nuclear@26 250 return crc ^ 0xffffffffUL;
nuclear@26 251 }
nuclear@26 252
nuclear@26 253 #ifdef BYFOUR
nuclear@26 254
nuclear@26 255 /* ========================================================================= */
nuclear@26 256 #define DOLIT4 c ^= *buf4++; \
nuclear@26 257 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
nuclear@26 258 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
nuclear@26 259 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
nuclear@26 260
nuclear@26 261 /* ========================================================================= */
nuclear@26 262 local unsigned long crc32_little(crc, buf, len)
nuclear@26 263 unsigned long crc;
nuclear@26 264 const unsigned char FAR *buf;
nuclear@26 265 unsigned len;
nuclear@26 266 {
nuclear@26 267 register u4 c;
nuclear@26 268 register const u4 FAR *buf4;
nuclear@26 269
nuclear@26 270 c = (u4)crc;
nuclear@26 271 c = ~c;
nuclear@26 272 while (len && ((ptrdiff_t)buf & 3)) {
nuclear@26 273 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
nuclear@26 274 len--;
nuclear@26 275 }
nuclear@26 276
nuclear@26 277 buf4 = (const u4 FAR *)(const void FAR *)buf;
nuclear@26 278 while (len >= 32) {
nuclear@26 279 DOLIT32;
nuclear@26 280 len -= 32;
nuclear@26 281 }
nuclear@26 282 while (len >= 4) {
nuclear@26 283 DOLIT4;
nuclear@26 284 len -= 4;
nuclear@26 285 }
nuclear@26 286 buf = (const unsigned char FAR *)buf4;
nuclear@26 287
nuclear@26 288 if (len) do {
nuclear@26 289 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
nuclear@26 290 } while (--len);
nuclear@26 291 c = ~c;
nuclear@26 292 return (unsigned long)c;
nuclear@26 293 }
nuclear@26 294
nuclear@26 295 /* ========================================================================= */
nuclear@26 296 #define DOBIG4 c ^= *++buf4; \
nuclear@26 297 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
nuclear@26 298 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
nuclear@26 299 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
nuclear@26 300
nuclear@26 301 /* ========================================================================= */
nuclear@26 302 local unsigned long crc32_big(crc, buf, len)
nuclear@26 303 unsigned long crc;
nuclear@26 304 const unsigned char FAR *buf;
nuclear@26 305 unsigned len;
nuclear@26 306 {
nuclear@26 307 register u4 c;
nuclear@26 308 register const u4 FAR *buf4;
nuclear@26 309
nuclear@26 310 c = REV((u4)crc);
nuclear@26 311 c = ~c;
nuclear@26 312 while (len && ((ptrdiff_t)buf & 3)) {
nuclear@26 313 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
nuclear@26 314 len--;
nuclear@26 315 }
nuclear@26 316
nuclear@26 317 buf4 = (const u4 FAR *)(const void FAR *)buf;
nuclear@26 318 buf4--;
nuclear@26 319 while (len >= 32) {
nuclear@26 320 DOBIG32;
nuclear@26 321 len -= 32;
nuclear@26 322 }
nuclear@26 323 while (len >= 4) {
nuclear@26 324 DOBIG4;
nuclear@26 325 len -= 4;
nuclear@26 326 }
nuclear@26 327 buf4++;
nuclear@26 328 buf = (const unsigned char FAR *)buf4;
nuclear@26 329
nuclear@26 330 if (len) do {
nuclear@26 331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
nuclear@26 332 } while (--len);
nuclear@26 333 c = ~c;
nuclear@26 334 return (unsigned long)(REV(c));
nuclear@26 335 }
nuclear@26 336
nuclear@26 337 #endif /* BYFOUR */
nuclear@26 338
nuclear@26 339 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
nuclear@26 340
nuclear@26 341 /* ========================================================================= */
nuclear@26 342 local unsigned long gf2_matrix_times(mat, vec)
nuclear@26 343 unsigned long *mat;
nuclear@26 344 unsigned long vec;
nuclear@26 345 {
nuclear@26 346 unsigned long sum;
nuclear@26 347
nuclear@26 348 sum = 0;
nuclear@26 349 while (vec) {
nuclear@26 350 if (vec & 1)
nuclear@26 351 sum ^= *mat;
nuclear@26 352 vec >>= 1;
nuclear@26 353 mat++;
nuclear@26 354 }
nuclear@26 355 return sum;
nuclear@26 356 }
nuclear@26 357
nuclear@26 358 /* ========================================================================= */
nuclear@26 359 local void gf2_matrix_square(square, mat)
nuclear@26 360 unsigned long *square;
nuclear@26 361 unsigned long *mat;
nuclear@26 362 {
nuclear@26 363 int n;
nuclear@26 364
nuclear@26 365 for (n = 0; n < GF2_DIM; n++)
nuclear@26 366 square[n] = gf2_matrix_times(mat, mat[n]);
nuclear@26 367 }
nuclear@26 368
nuclear@26 369 /* ========================================================================= */
nuclear@26 370 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
nuclear@26 371 uLong crc1;
nuclear@26 372 uLong crc2;
nuclear@26 373 z_off_t len2;
nuclear@26 374 {
nuclear@26 375 int n;
nuclear@26 376 unsigned long row;
nuclear@26 377 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
nuclear@26 378 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
nuclear@26 379
nuclear@26 380 /* degenerate case */
nuclear@26 381 if (len2 == 0)
nuclear@26 382 return crc1;
nuclear@26 383
nuclear@26 384 /* put operator for one zero bit in odd */
nuclear@26 385 odd[0] = 0xedb88320L; /* CRC-32 polynomial */
nuclear@26 386 row = 1;
nuclear@26 387 for (n = 1; n < GF2_DIM; n++) {
nuclear@26 388 odd[n] = row;
nuclear@26 389 row <<= 1;
nuclear@26 390 }
nuclear@26 391
nuclear@26 392 /* put operator for two zero bits in even */
nuclear@26 393 gf2_matrix_square(even, odd);
nuclear@26 394
nuclear@26 395 /* put operator for four zero bits in odd */
nuclear@26 396 gf2_matrix_square(odd, even);
nuclear@26 397
nuclear@26 398 /* apply len2 zeros to crc1 (first square will put the operator for one
nuclear@26 399 zero byte, eight zero bits, in even) */
nuclear@26 400 do {
nuclear@26 401 /* apply zeros operator for this bit of len2 */
nuclear@26 402 gf2_matrix_square(even, odd);
nuclear@26 403 if (len2 & 1)
nuclear@26 404 crc1 = gf2_matrix_times(even, crc1);
nuclear@26 405 len2 >>= 1;
nuclear@26 406
nuclear@26 407 /* if no more bits set, then done */
nuclear@26 408 if (len2 == 0)
nuclear@26 409 break;
nuclear@26 410
nuclear@26 411 /* another iteration of the loop with odd and even swapped */
nuclear@26 412 gf2_matrix_square(odd, even);
nuclear@26 413 if (len2 & 1)
nuclear@26 414 crc1 = gf2_matrix_times(odd, crc1);
nuclear@26 415 len2 >>= 1;
nuclear@26 416
nuclear@26 417 /* if no more bits set, then done */
nuclear@26 418 } while (len2 != 0);
nuclear@26 419
nuclear@26 420 /* return combined crc */
nuclear@26 421 crc1 ^= crc2;
nuclear@26 422 return crc1;
nuclear@26 423 }