Annotation of embedaddon/rsync/zlib/crc32.c, revision 1.1.1.3
1.1 misho 1: /* crc32.c -- compute the CRC-32 of a data stream
1.1.1.2 misho 2: * Copyright (C) 1995-2006, 2010, 2011, 2012 Mark Adler
1.1 misho 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().
1.1.1.2 misho 20:
21: DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h.
1.1 misho 22: */
23:
24: #ifdef MAKECRCH
25: # include <stdio.h>
26: # ifndef DYNAMIC_CRC_TABLE
27: # define DYNAMIC_CRC_TABLE
28: # endif /* !DYNAMIC_CRC_TABLE */
29: #endif /* MAKECRCH */
30:
31: #include "zutil.h" /* for STDC and FAR definitions */
32:
33: #define local static
34:
35: /* Definitions for doing the crc four data bytes at a time. */
1.1.1.2 misho 36: #if !defined(NOBYFOUR) && defined(Z_U4)
37: # define BYFOUR
38: #endif
1.1 misho 39: #ifdef BYFOUR
40: local unsigned long crc32_little OF((unsigned long,
41: const unsigned char FAR *, unsigned));
42: local unsigned long crc32_big OF((unsigned long,
43: const unsigned char FAR *, unsigned));
44: # define TBLS 8
45: #else
46: # define TBLS 1
47: #endif /* BYFOUR */
48:
49: /* Local functions for crc concatenation */
50: local unsigned long gf2_matrix_times OF((unsigned long *mat,
51: unsigned long vec));
52: local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
1.1.1.2 misho 53: local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
54:
1.1 misho 55:
56: #ifdef DYNAMIC_CRC_TABLE
57:
58: local volatile int crc_table_empty = 1;
1.1.1.2 misho 59: local z_crc_t FAR crc_table[TBLS][256];
1.1 misho 60: local void make_crc_table OF((void));
61: #ifdef MAKECRCH
1.1.1.2 misho 62: local void write_table OF((FILE *, const z_crc_t FAR *));
1.1 misho 63: #endif /* MAKECRCH */
64: /*
65: Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
66: 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.
67:
68: Polynomials over GF(2) are represented in binary, one bit per coefficient,
69: with the lowest powers in the most significant bit. Then adding polynomials
70: is just exclusive-or, and multiplying a polynomial by x is a right shift by
71: one. If we call the above polynomial p, and represent a byte as the
72: polynomial q, also with the lowest power in the most significant bit (so the
73: byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
74: where a mod b means the remainder after dividing a by b.
75:
76: This calculation is done using the shift-register method of multiplying and
77: taking the remainder. The register is initialized to zero, and for each
78: incoming bit, x^32 is added mod p to the register if the bit is a one (where
79: x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
80: x (which is shifting right by one and adding x^32 mod p if the bit shifted
81: out is a one). We start with the highest power (least significant bit) of
82: q and repeat for all eight bits of q.
83:
84: The first table is simply the CRC of all possible eight bit values. This is
85: all the information needed to generate CRCs on data a byte at a time for all
86: combinations of CRC register values and incoming bytes. The remaining tables
87: allow for word-at-a-time CRC calculation for both big-endian and little-
88: endian machines, where a word is four bytes.
89: */
90: local void make_crc_table()
91: {
1.1.1.2 misho 92: z_crc_t c;
1.1 misho 93: int n, k;
1.1.1.2 misho 94: z_crc_t poly; /* polynomial exclusive-or pattern */
1.1 misho 95: /* terms of polynomial defining this crc (except x^32): */
96: static volatile int first = 1; /* flag to limit concurrent making */
97: static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
98:
99: /* See if another task is already doing this (not thread-safe, but better
100: than nothing -- significantly reduces duration of vulnerability in
101: case the advice about DYNAMIC_CRC_TABLE is ignored) */
102: if (first) {
103: first = 0;
104:
105: /* make exclusive-or pattern from polynomial (0xedb88320UL) */
1.1.1.2 misho 106: poly = 0;
107: for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
108: poly |= (z_crc_t)1 << (31 - p[n]);
1.1 misho 109:
110: /* generate a crc for every 8-bit value */
111: for (n = 0; n < 256; n++) {
1.1.1.2 misho 112: c = (z_crc_t)n;
1.1 misho 113: for (k = 0; k < 8; k++)
114: c = c & 1 ? poly ^ (c >> 1) : c >> 1;
115: crc_table[0][n] = c;
116: }
117:
118: #ifdef BYFOUR
119: /* generate crc for each value followed by one, two, and three zeros,
120: and then the byte reversal of those as well as the first table */
121: for (n = 0; n < 256; n++) {
122: c = crc_table[0][n];
1.1.1.2 misho 123: crc_table[4][n] = ZSWAP32(c);
1.1 misho 124: for (k = 1; k < 4; k++) {
125: c = crc_table[0][c & 0xff] ^ (c >> 8);
126: crc_table[k][n] = c;
1.1.1.2 misho 127: crc_table[k + 4][n] = ZSWAP32(c);
1.1 misho 128: }
129: }
130: #endif /* BYFOUR */
131:
132: crc_table_empty = 0;
133: }
134: else { /* not first */
135: /* wait for the other guy to finish (not efficient, but rare) */
136: while (crc_table_empty)
137: ;
138: }
139:
140: #ifdef MAKECRCH
141: /* write out CRC tables to crc32.h */
142: {
143: FILE *out;
144:
145: out = fopen("crc32.h", "w");
146: if (out == NULL) return;
147: fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
148: fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
1.1.1.2 misho 149: fprintf(out, "local const z_crc_t FAR ");
1.1 misho 150: fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
151: write_table(out, crc_table[0]);
152: # ifdef BYFOUR
153: fprintf(out, "#ifdef BYFOUR\n");
154: for (k = 1; k < 8; k++) {
155: fprintf(out, " },\n {\n");
156: write_table(out, crc_table[k]);
157: }
158: fprintf(out, "#endif\n");
159: # endif /* BYFOUR */
160: fprintf(out, " }\n};\n");
161: fclose(out);
162: }
163: #endif /* MAKECRCH */
164: }
165:
166: #ifdef MAKECRCH
167: local void write_table(out, table)
168: FILE *out;
1.1.1.2 misho 169: const z_crc_t FAR *table;
1.1 misho 170: {
171: int n;
172:
173: for (n = 0; n < 256; n++)
1.1.1.2 misho 174: fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
175: (unsigned long)(table[n]),
1.1 misho 176: n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
177: }
178: #endif /* MAKECRCH */
179:
180: #else /* !DYNAMIC_CRC_TABLE */
181: /* ========================================================================
182: * Tables of CRC-32s of all single-byte values, made by make_crc_table().
183: */
184: #include "crc32.h"
185: #endif /* DYNAMIC_CRC_TABLE */
186:
187: /* =========================================================================
188: * This function can be used by asm versions of crc32()
189: */
1.1.1.2 misho 190: const z_crc_t FAR * ZEXPORT get_crc_table()
1.1 misho 191: {
192: #ifdef DYNAMIC_CRC_TABLE
193: if (crc_table_empty)
194: make_crc_table();
195: #endif /* DYNAMIC_CRC_TABLE */
1.1.1.2 misho 196: return (const z_crc_t FAR *)crc_table;
1.1 misho 197: }
198:
199: /* ========================================================================= */
200: #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
201: #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
202:
203: /* ========================================================================= */
204: unsigned long ZEXPORT crc32(crc, buf, len)
205: unsigned long crc;
206: const unsigned char FAR *buf;
1.1.1.2 misho 207: uInt len;
1.1 misho 208: {
209: if (buf == Z_NULL) return 0UL;
210:
211: #ifdef DYNAMIC_CRC_TABLE
212: if (crc_table_empty)
213: make_crc_table();
214: #endif /* DYNAMIC_CRC_TABLE */
215:
216: #ifdef BYFOUR
217: if (sizeof(void *) == sizeof(ptrdiff_t)) {
1.1.1.2 misho 218: z_crc_t endian;
1.1 misho 219:
220: endian = 1;
221: if (*((unsigned char *)(&endian)))
222: return crc32_little(crc, buf, len);
223: else
224: return crc32_big(crc, buf, len);
225: }
226: #endif /* BYFOUR */
227: crc = crc ^ 0xffffffffUL;
228: while (len >= 8) {
229: DO8;
230: len -= 8;
231: }
232: if (len) do {
233: DO1;
234: } while (--len);
235: return crc ^ 0xffffffffUL;
236: }
237:
238: #ifdef BYFOUR
239:
240: /* ========================================================================= */
241: #define DOLIT4 c ^= *buf4++; \
242: c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
243: crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
244: #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
245:
246: /* ========================================================================= */
247: local unsigned long crc32_little(crc, buf, len)
248: unsigned long crc;
249: const unsigned char FAR *buf;
250: unsigned len;
251: {
1.1.1.2 misho 252: register z_crc_t c;
253: register const z_crc_t FAR *buf4;
1.1 misho 254:
1.1.1.2 misho 255: c = (z_crc_t)crc;
1.1 misho 256: c = ~c;
257: while (len && ((ptrdiff_t)buf & 3)) {
258: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
259: len--;
260: }
261:
1.1.1.2 misho 262: buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
1.1 misho 263: while (len >= 32) {
264: DOLIT32;
265: len -= 32;
266: }
267: while (len >= 4) {
268: DOLIT4;
269: len -= 4;
270: }
271: buf = (const unsigned char FAR *)buf4;
272:
273: if (len) do {
274: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
275: } while (--len);
276: c = ~c;
277: return (unsigned long)c;
278: }
279:
280: /* ========================================================================= */
1.1.1.3 ! misho 281: #define DOBIG4 c ^= *buf4++; \
1.1 misho 282: c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
283: crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
284: #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
285:
286: /* ========================================================================= */
287: local unsigned long crc32_big(crc, buf, len)
288: unsigned long crc;
289: const unsigned char FAR *buf;
290: unsigned len;
291: {
1.1.1.2 misho 292: register z_crc_t c;
293: register const z_crc_t FAR *buf4;
1.1 misho 294:
1.1.1.2 misho 295: c = ZSWAP32((z_crc_t)crc);
1.1 misho 296: c = ~c;
297: while (len && ((ptrdiff_t)buf & 3)) {
298: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
299: len--;
300: }
301:
1.1.1.2 misho 302: buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
1.1 misho 303: while (len >= 32) {
304: DOBIG32;
305: len -= 32;
306: }
307: while (len >= 4) {
308: DOBIG4;
309: len -= 4;
310: }
311: buf = (const unsigned char FAR *)buf4;
312:
313: if (len) do {
314: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
315: } while (--len);
316: c = ~c;
1.1.1.2 misho 317: return (unsigned long)(ZSWAP32(c));
1.1 misho 318: }
319:
320: #endif /* BYFOUR */
321:
322: #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
323:
324: /* ========================================================================= */
325: local unsigned long gf2_matrix_times(mat, vec)
326: unsigned long *mat;
327: unsigned long vec;
328: {
329: unsigned long sum;
330:
331: sum = 0;
332: while (vec) {
333: if (vec & 1)
334: sum ^= *mat;
335: vec >>= 1;
336: mat++;
337: }
338: return sum;
339: }
340:
341: /* ========================================================================= */
342: local void gf2_matrix_square(square, mat)
343: unsigned long *square;
344: unsigned long *mat;
345: {
346: int n;
347:
348: for (n = 0; n < GF2_DIM; n++)
349: square[n] = gf2_matrix_times(mat, mat[n]);
350: }
351:
352: /* ========================================================================= */
1.1.1.2 misho 353: local uLong crc32_combine_(crc1, crc2, len2)
1.1 misho 354: uLong crc1;
355: uLong crc2;
1.1.1.2 misho 356: z_off64_t len2;
1.1 misho 357: {
358: int n;
359: unsigned long row;
360: unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
361: unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
362:
1.1.1.2 misho 363: /* degenerate case (also disallow negative lengths) */
364: if (len2 <= 0)
1.1 misho 365: return crc1;
366:
367: /* put operator for one zero bit in odd */
1.1.1.2 misho 368: odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
1.1 misho 369: row = 1;
370: for (n = 1; n < GF2_DIM; n++) {
371: odd[n] = row;
372: row <<= 1;
373: }
374:
375: /* put operator for two zero bits in even */
376: gf2_matrix_square(even, odd);
377:
378: /* put operator for four zero bits in odd */
379: gf2_matrix_square(odd, even);
380:
381: /* apply len2 zeros to crc1 (first square will put the operator for one
382: zero byte, eight zero bits, in even) */
383: do {
384: /* apply zeros operator for this bit of len2 */
385: gf2_matrix_square(even, odd);
386: if (len2 & 1)
387: crc1 = gf2_matrix_times(even, crc1);
388: len2 >>= 1;
389:
390: /* if no more bits set, then done */
391: if (len2 == 0)
392: break;
393:
394: /* another iteration of the loop with odd and even swapped */
395: gf2_matrix_square(odd, even);
396: if (len2 & 1)
397: crc1 = gf2_matrix_times(odd, crc1);
398: len2 >>= 1;
399:
400: /* if no more bits set, then done */
401: } while (len2 != 0);
402:
403: /* return combined crc */
404: crc1 ^= crc2;
405: return crc1;
406: }
1.1.1.2 misho 407:
408: /* ========================================================================= */
409: uLong ZEXPORT crc32_combine(crc1, crc2, len2)
410: uLong crc1;
411: uLong crc2;
412: z_off_t len2;
413: {
414: return crc32_combine_(crc1, crc2, len2);
415: }
416:
417: uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
418: uLong crc1;
419: uLong crc2;
420: z_off64_t len2;
421: {
422: return crc32_combine_(crc1, crc2, len2);
423: }
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