Annotation of embedaddon/sudo/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) 1995-2006, 2010 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)&0xff)+(((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: local uLong crc32_combine_(uLong crc1, uLong crc2, z_off64_t len2);
72:
73:
74: #ifdef DYNAMIC_CRC_TABLE
75:
76: local volatile int crc_table_empty = 1;
77: local unsigned long FAR crc_table[TBLS][256];
78: local void make_crc_table OF((void));
79: #ifdef MAKECRCH
80: local void write_table OF((FILE *, const unsigned long FAR *));
81: #endif /* MAKECRCH */
82: /*
83: Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
84: 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.
85:
86: Polynomials over GF(2) are represented in binary, one bit per coefficient,
87: with the lowest powers in the most significant bit. Then adding polynomials
88: is just exclusive-or, and multiplying a polynomial by x is a right shift by
89: one. If we call the above polynomial p, and represent a byte as the
90: polynomial q, also with the lowest power in the most significant bit (so the
91: byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
92: where a mod b means the remainder after dividing a by b.
93:
94: This calculation is done using the shift-register method of multiplying and
95: taking the remainder. The register is initialized to zero, and for each
96: incoming bit, x^32 is added mod p to the register if the bit is a one (where
97: x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
98: x (which is shifting right by one and adding x^32 mod p if the bit shifted
99: out is a one). We start with the highest power (least significant bit) of
100: q and repeat for all eight bits of q.
101:
102: The first table is simply the CRC of all possible eight bit values. This is
103: all the information needed to generate CRCs on data a byte at a time for all
104: combinations of CRC register values and incoming bytes. The remaining tables
105: allow for word-at-a-time CRC calculation for both big-endian and little-
106: endian machines, where a word is four bytes.
107: */
108: local void make_crc_table()
109: {
110: unsigned long c;
111: int n, k;
112: unsigned long poly; /* polynomial exclusive-or pattern */
113: /* terms of polynomial defining this crc (except x^32): */
114: static volatile int first = 1; /* flag to limit concurrent making */
115: static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
116:
117: /* See if another task is already doing this (not thread-safe, but better
118: than nothing -- significantly reduces duration of vulnerability in
119: case the advice about DYNAMIC_CRC_TABLE is ignored) */
120: if (first) {
121: first = 0;
122:
123: /* make exclusive-or pattern from polynomial (0xedb88320UL) */
124: poly = 0UL;
125: for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
126: poly |= 1UL << (31 - p[n]);
127:
128: /* generate a crc for every 8-bit value */
129: for (n = 0; n < 256; n++) {
130: c = (unsigned long)n;
131: for (k = 0; k < 8; k++)
132: c = c & 1 ? poly ^ (c >> 1) : c >> 1;
133: crc_table[0][n] = c;
134: }
135:
136: #ifdef BYFOUR
137: /* generate crc for each value followed by one, two, and three zeros,
138: and then the byte reversal of those as well as the first table */
139: for (n = 0; n < 256; n++) {
140: c = crc_table[0][n];
141: crc_table[4][n] = REV(c);
142: for (k = 1; k < 4; k++) {
143: c = crc_table[0][c & 0xff] ^ (c >> 8);
144: crc_table[k][n] = c;
145: crc_table[k + 4][n] = REV(c);
146: }
147: }
148: #endif /* BYFOUR */
149:
150: crc_table_empty = 0;
151: }
152: else { /* not first */
153: /* wait for the other guy to finish (not efficient, but rare) */
154: while (crc_table_empty)
155: ;
156: }
157:
158: #ifdef MAKECRCH
159: /* write out CRC tables to crc32.h */
160: {
161: FILE *out;
162:
163: out = fopen("crc32.h", "w");
164: if (out == NULL) return;
165: fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
166: fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
167: fprintf(out, "local const unsigned long FAR ");
168: fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
169: write_table(out, crc_table[0]);
170: # ifdef BYFOUR
171: fprintf(out, "#ifdef BYFOUR\n");
172: for (k = 1; k < 8; k++) {
173: fprintf(out, " },\n {\n");
174: write_table(out, crc_table[k]);
175: }
176: fprintf(out, "#endif\n");
177: # endif /* BYFOUR */
178: fprintf(out, " }\n};\n");
179: fclose(out);
180: }
181: #endif /* MAKECRCH */
182: }
183:
184: #ifdef MAKECRCH
185: local void write_table(out, table)
186: FILE *out;
187: const unsigned long FAR *table;
188: {
189: int n;
190:
191: for (n = 0; n < 256; n++)
192: fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ", table[n],
193: n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
194: }
195: #endif /* MAKECRCH */
196:
197: #else /* !DYNAMIC_CRC_TABLE */
198: /* ========================================================================
199: * Tables of CRC-32s of all single-byte values, made by make_crc_table().
200: */
201: #include "crc32.h"
202: #endif /* DYNAMIC_CRC_TABLE */
203:
204: /* =========================================================================
205: * This function can be used by asm versions of crc32()
206: */
207: const unsigned long FAR * ZEXPORT get_crc_table()
208: {
209: #ifdef DYNAMIC_CRC_TABLE
210: if (crc_table_empty)
211: make_crc_table();
212: #endif /* DYNAMIC_CRC_TABLE */
213: return (const unsigned long FAR *)crc_table;
214: }
215:
216: /* ========================================================================= */
217: #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
218: #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
219:
220: /* ========================================================================= */
221: unsigned long ZEXPORT crc32(crc, buf, len)
222: unsigned long crc;
223: const unsigned char FAR *buf;
224: uInt len;
225: {
226: if (buf == Z_NULL) return 0UL;
227:
228: #ifdef DYNAMIC_CRC_TABLE
229: if (crc_table_empty)
230: make_crc_table();
231: #endif /* DYNAMIC_CRC_TABLE */
232:
233: #ifdef BYFOUR
234: if (sizeof(void *) == sizeof(ptrdiff_t)) {
235: u4 endian;
236:
237: endian = 1;
238: if (*((unsigned char *)(&endian)))
239: return crc32_little(crc, buf, len);
240: else
241: return crc32_big(crc, buf, len);
242: }
243: #endif /* BYFOUR */
244: crc = crc ^ 0xffffffffUL;
245: while (len >= 8) {
246: DO8;
247: len -= 8;
248: }
249: if (len) do {
250: DO1;
251: } while (--len);
252: return crc ^ 0xffffffffUL;
253: }
254:
255: #ifdef BYFOUR
256:
257: /* ========================================================================= */
258: #define DOLIT4 c ^= *buf4++; \
259: c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
260: crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
261: #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
262:
263: /* ========================================================================= */
264: local unsigned long crc32_little(crc, buf, len)
265: unsigned long crc;
266: const unsigned char FAR *buf;
267: unsigned len;
268: {
269: register u4 c;
270: register const u4 FAR *buf4;
271:
272: c = (u4)crc;
273: c = ~c;
274: while (len && ((ptrdiff_t)buf & 3)) {
275: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
276: len--;
277: }
278:
279: buf4 = (const u4 FAR *)(const void FAR *)buf;
280: while (len >= 32) {
281: DOLIT32;
282: len -= 32;
283: }
284: while (len >= 4) {
285: DOLIT4;
286: len -= 4;
287: }
288: buf = (const unsigned char FAR *)buf4;
289:
290: if (len) do {
291: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
292: } while (--len);
293: c = ~c;
294: return (unsigned long)c;
295: }
296:
297: /* ========================================================================= */
298: #define DOBIG4 c ^= *++buf4; \
299: c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
300: crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
301: #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
302:
303: /* ========================================================================= */
304: local unsigned long crc32_big(crc, buf, len)
305: unsigned long crc;
306: const unsigned char FAR *buf;
307: unsigned len;
308: {
309: register u4 c;
310: register const u4 FAR *buf4;
311:
312: c = REV((u4)crc);
313: c = ~c;
314: while (len && ((ptrdiff_t)buf & 3)) {
315: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
316: len--;
317: }
318:
319: buf4 = (const u4 FAR *)(const void FAR *)buf;
320: buf4--;
321: while (len >= 32) {
322: DOBIG32;
323: len -= 32;
324: }
325: while (len >= 4) {
326: DOBIG4;
327: len -= 4;
328: }
329: buf4++;
330: buf = (const unsigned char FAR *)buf4;
331:
332: if (len) do {
333: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
334: } while (--len);
335: c = ~c;
336: return (unsigned long)(REV(c));
337: }
338:
339: #endif /* BYFOUR */
340:
341: #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
342:
343: /* ========================================================================= */
344: local unsigned long gf2_matrix_times(mat, vec)
345: unsigned long *mat;
346: unsigned long vec;
347: {
348: unsigned long sum;
349:
350: sum = 0;
351: while (vec) {
352: if (vec & 1)
353: sum ^= *mat;
354: vec >>= 1;
355: mat++;
356: }
357: return sum;
358: }
359:
360: /* ========================================================================= */
361: local void gf2_matrix_square(square, mat)
362: unsigned long *square;
363: unsigned long *mat;
364: {
365: int n;
366:
367: for (n = 0; n < GF2_DIM; n++)
368: square[n] = gf2_matrix_times(mat, mat[n]);
369: }
370:
371: /* ========================================================================= */
372: local uLong crc32_combine_(crc1, crc2, len2)
373: uLong crc1;
374: uLong crc2;
375: z_off64_t len2;
376: {
377: int n;
378: unsigned long row;
379: unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
380: unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
381:
382: /* degenerate case (also disallow negative lengths) */
383: if (len2 <= 0)
384: return crc1;
385:
386: /* put operator for one zero bit in odd */
387: odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
388: row = 1;
389: for (n = 1; n < GF2_DIM; n++) {
390: odd[n] = row;
391: row <<= 1;
392: }
393:
394: /* put operator for two zero bits in even */
395: gf2_matrix_square(even, odd);
396:
397: /* put operator for four zero bits in odd */
398: gf2_matrix_square(odd, even);
399:
400: /* apply len2 zeros to crc1 (first square will put the operator for one
401: zero byte, eight zero bits, in even) */
402: do {
403: /* apply zeros operator for this bit of len2 */
404: gf2_matrix_square(even, odd);
405: if (len2 & 1)
406: crc1 = gf2_matrix_times(even, crc1);
407: len2 >>= 1;
408:
409: /* if no more bits set, then done */
410: if (len2 == 0)
411: break;
412:
413: /* another iteration of the loop with odd and even swapped */
414: gf2_matrix_square(odd, even);
415: if (len2 & 1)
416: crc1 = gf2_matrix_times(odd, crc1);
417: len2 >>= 1;
418:
419: /* if no more bits set, then done */
420: } while (len2 != 0);
421:
422: /* return combined crc */
423: crc1 ^= crc2;
424: return crc1;
425: }
426:
427: /* ========================================================================= */
428: uLong ZEXPORT crc32_combine(crc1, crc2, len2)
429: uLong crc1;
430: uLong crc2;
431: z_off_t len2;
432: {
433: return crc32_combine_(crc1, crc2, len2);
434: }
435:
436: uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
437: uLong crc1;
438: uLong crc2;
439: z_off64_t len2;
440: {
441: return crc32_combine_(crc1, crc2, len2);
442: }
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