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