Annotation of embedaddon/rsync/zlib/crc32.c, revision 1.1.1.1
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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