Annotation of embedaddon/sudo/zlib/crc32.c, revision 1.1.1.2
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 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: /* Find a four-byte integer type for crc32_little() and crc32_big(). */
36: #ifndef NOBYFOUR
37: # ifdef STDC /* need ANSI C limits.h to determine sizes */
38: # include <limits.h>
39: # define BYFOUR
40: # if (UINT_MAX == 0xffffffffUL)
41: typedef unsigned int u4;
42: # else
43: # if (ULONG_MAX == 0xffffffffUL)
44: typedef unsigned long u4;
45: # else
46: # if (USHRT_MAX == 0xffffffffUL)
47: typedef unsigned short u4;
48: # else
49: # undef BYFOUR /* can't find a four-byte integer type! */
50: # endif
51: # endif
52: # endif
53: # endif /* STDC */
54: #endif /* !NOBYFOUR */
55:
56: /* Definitions for doing the crc four data bytes at a time. */
57: #ifdef BYFOUR
1.1.1.2 ! misho 58: typedef u4 crc_table_t;
1.1 misho 59: # define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
60: (((w)&0xff00)<<8)+(((w)&0xff)<<24))
61: local unsigned long crc32_little OF((unsigned long,
62: const unsigned char FAR *, unsigned));
63: local unsigned long crc32_big OF((unsigned long,
64: const unsigned char FAR *, unsigned));
65: # define TBLS 8
66: #else
1.1.1.2 ! misho 67: typedef unsigned long crc_table_t;
1.1 misho 68: # define TBLS 1
69: #endif /* BYFOUR */
70:
71: /* Local functions for crc concatenation */
72: local unsigned long gf2_matrix_times OF((unsigned long *mat,
73: unsigned long vec));
74: local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
1.1.1.2 ! misho 75: local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
1.1 misho 76:
77:
78: #ifdef DYNAMIC_CRC_TABLE
79:
80: local volatile int crc_table_empty = 1;
1.1.1.2 ! misho 81: local crc_table_t FAR crc_table[TBLS][256];
1.1 misho 82: local void make_crc_table OF((void));
83: #ifdef MAKECRCH
1.1.1.2 ! misho 84: local void write_table OF((FILE *, const crc_table_t FAR *));
1.1 misho 85: #endif /* MAKECRCH */
86: /*
87: Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
88: 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.
89:
90: Polynomials over GF(2) are represented in binary, one bit per coefficient,
91: with the lowest powers in the most significant bit. Then adding polynomials
92: is just exclusive-or, and multiplying a polynomial by x is a right shift by
93: one. If we call the above polynomial p, and represent a byte as the
94: polynomial q, also with the lowest power in the most significant bit (so the
95: byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
96: where a mod b means the remainder after dividing a by b.
97:
98: This calculation is done using the shift-register method of multiplying and
99: taking the remainder. The register is initialized to zero, and for each
100: incoming bit, x^32 is added mod p to the register if the bit is a one (where
101: x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
102: x (which is shifting right by one and adding x^32 mod p if the bit shifted
103: out is a one). We start with the highest power (least significant bit) of
104: q and repeat for all eight bits of q.
105:
106: The first table is simply the CRC of all possible eight bit values. This is
107: all the information needed to generate CRCs on data a byte at a time for all
108: combinations of CRC register values and incoming bytes. The remaining tables
109: allow for word-at-a-time CRC calculation for both big-endian and little-
110: endian machines, where a word is four bytes.
111: */
112: local void make_crc_table()
113: {
1.1.1.2 ! misho 114: crc_table_t c;
1.1 misho 115: int n, k;
1.1.1.2 ! misho 116: crc_table_t poly; /* polynomial exclusive-or pattern */
1.1 misho 117: /* terms of polynomial defining this crc (except x^32): */
118: static volatile int first = 1; /* flag to limit concurrent making */
119: static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
120:
121: /* See if another task is already doing this (not thread-safe, but better
122: than nothing -- significantly reduces duration of vulnerability in
123: case the advice about DYNAMIC_CRC_TABLE is ignored) */
124: if (first) {
125: first = 0;
126:
127: /* make exclusive-or pattern from polynomial (0xedb88320UL) */
1.1.1.2 ! misho 128: poly = 0;
! 129: for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
! 130: poly |= (crc_table_t)1 << (31 - p[n]);
1.1 misho 131:
132: /* generate a crc for every 8-bit value */
133: for (n = 0; n < 256; n++) {
1.1.1.2 ! misho 134: c = (crc_table_t)n;
1.1 misho 135: for (k = 0; k < 8; k++)
136: c = c & 1 ? poly ^ (c >> 1) : c >> 1;
137: crc_table[0][n] = c;
138: }
139:
140: #ifdef BYFOUR
141: /* generate crc for each value followed by one, two, and three zeros,
142: and then the byte reversal of those as well as the first table */
143: for (n = 0; n < 256; n++) {
144: c = crc_table[0][n];
145: crc_table[4][n] = REV(c);
146: for (k = 1; k < 4; k++) {
147: c = crc_table[0][c & 0xff] ^ (c >> 8);
148: crc_table[k][n] = c;
149: crc_table[k + 4][n] = REV(c);
150: }
151: }
152: #endif /* BYFOUR */
153:
154: crc_table_empty = 0;
155: }
156: else { /* not first */
157: /* wait for the other guy to finish (not efficient, but rare) */
158: while (crc_table_empty)
159: ;
160: }
161:
162: #ifdef MAKECRCH
163: /* write out CRC tables to crc32.h */
164: {
165: FILE *out;
166:
167: out = fopen("crc32.h", "w");
168: if (out == NULL) return;
169: fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
170: fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
1.1.1.2 ! misho 171: fprintf(out, "local const crc_table_t FAR ");
1.1 misho 172: fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
173: write_table(out, crc_table[0]);
174: # ifdef BYFOUR
175: fprintf(out, "#ifdef BYFOUR\n");
176: for (k = 1; k < 8; k++) {
177: fprintf(out, " },\n {\n");
178: write_table(out, crc_table[k]);
179: }
180: fprintf(out, "#endif\n");
181: # endif /* BYFOUR */
182: fprintf(out, " }\n};\n");
183: fclose(out);
184: }
185: #endif /* MAKECRCH */
186: }
187:
188: #ifdef MAKECRCH
189: local void write_table(out, table)
190: FILE *out;
1.1.1.2 ! misho 191: const crc_table_t FAR *table;
1.1 misho 192: {
193: int n;
194:
195: for (n = 0; n < 256; n++)
1.1.1.2 ! misho 196: fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
! 197: (unsigned long)(table[n]),
1.1 misho 198: n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
199: }
200: #endif /* MAKECRCH */
201:
202: #else /* !DYNAMIC_CRC_TABLE */
203: /* ========================================================================
204: * Tables of CRC-32s of all single-byte values, made by make_crc_table().
205: */
206: #include "crc32.h"
207: #endif /* DYNAMIC_CRC_TABLE */
208:
209: /* =========================================================================
210: * This function can be used by asm versions of crc32()
211: */
212: const unsigned long FAR * ZEXPORT get_crc_table()
213: {
214: #ifdef DYNAMIC_CRC_TABLE
215: if (crc_table_empty)
216: make_crc_table();
217: #endif /* DYNAMIC_CRC_TABLE */
1.1.1.2 ! misho 218: return (const unsigned long FAR *)(void FAR *)crc_table;
1.1 misho 219: }
220:
221: /* ========================================================================= */
222: #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
223: #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
224:
225: /* ========================================================================= */
226: unsigned long ZEXPORT crc32(crc, buf, len)
227: unsigned long crc;
228: const unsigned char FAR *buf;
229: uInt len;
230: {
231: if (buf == Z_NULL) return 0UL;
232:
233: #ifdef DYNAMIC_CRC_TABLE
234: if (crc_table_empty)
235: make_crc_table();
236: #endif /* DYNAMIC_CRC_TABLE */
237:
238: #ifdef BYFOUR
239: if (sizeof(void *) == sizeof(ptrdiff_t)) {
240: u4 endian;
241:
242: endian = 1;
243: if (*((unsigned char *)(&endian)))
244: return crc32_little(crc, buf, len);
245: else
246: return crc32_big(crc, buf, len);
247: }
248: #endif /* BYFOUR */
249: crc = crc ^ 0xffffffffUL;
250: while (len >= 8) {
251: DO8;
252: len -= 8;
253: }
254: if (len) do {
255: DO1;
256: } while (--len);
257: return crc ^ 0xffffffffUL;
258: }
259:
260: #ifdef BYFOUR
261:
262: /* ========================================================================= */
263: #define DOLIT4 c ^= *buf4++; \
264: c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
265: crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
266: #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
267:
268: /* ========================================================================= */
269: local unsigned long crc32_little(crc, buf, len)
270: unsigned long crc;
271: const unsigned char FAR *buf;
272: unsigned len;
273: {
274: register u4 c;
275: register const u4 FAR *buf4;
276:
277: c = (u4)crc;
278: c = ~c;
279: while (len && ((ptrdiff_t)buf & 3)) {
280: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
281: len--;
282: }
283:
284: buf4 = (const u4 FAR *)(const void FAR *)buf;
285: while (len >= 32) {
286: DOLIT32;
287: len -= 32;
288: }
289: while (len >= 4) {
290: DOLIT4;
291: len -= 4;
292: }
293: buf = (const unsigned char FAR *)buf4;
294:
295: if (len) do {
296: c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
297: } while (--len);
298: c = ~c;
299: return (unsigned long)c;
300: }
301:
302: /* ========================================================================= */
303: #define DOBIG4 c ^= *++buf4; \
304: c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
305: crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
306: #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
307:
308: /* ========================================================================= */
309: local unsigned long crc32_big(crc, buf, len)
310: unsigned long crc;
311: const unsigned char FAR *buf;
312: unsigned len;
313: {
314: register u4 c;
315: register const u4 FAR *buf4;
316:
317: c = REV((u4)crc);
318: c = ~c;
319: while (len && ((ptrdiff_t)buf & 3)) {
320: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
321: len--;
322: }
323:
324: buf4 = (const u4 FAR *)(const void FAR *)buf;
325: buf4--;
326: while (len >= 32) {
327: DOBIG32;
328: len -= 32;
329: }
330: while (len >= 4) {
331: DOBIG4;
332: len -= 4;
333: }
334: buf4++;
335: buf = (const unsigned char FAR *)buf4;
336:
337: if (len) do {
338: c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
339: } while (--len);
340: c = ~c;
341: return (unsigned long)(REV(c));
342: }
343:
344: #endif /* BYFOUR */
345:
346: #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
347:
348: /* ========================================================================= */
349: local unsigned long gf2_matrix_times(mat, vec)
350: unsigned long *mat;
351: unsigned long vec;
352: {
353: unsigned long sum;
354:
355: sum = 0;
356: while (vec) {
357: if (vec & 1)
358: sum ^= *mat;
359: vec >>= 1;
360: mat++;
361: }
362: return sum;
363: }
364:
365: /* ========================================================================= */
366: local void gf2_matrix_square(square, mat)
367: unsigned long *square;
368: unsigned long *mat;
369: {
370: int n;
371:
372: for (n = 0; n < GF2_DIM; n++)
373: square[n] = gf2_matrix_times(mat, mat[n]);
374: }
375:
376: /* ========================================================================= */
377: local uLong crc32_combine_(crc1, crc2, len2)
378: uLong crc1;
379: uLong crc2;
380: z_off64_t len2;
381: {
382: int n;
383: unsigned long row;
384: unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
385: unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
386:
387: /* degenerate case (also disallow negative lengths) */
388: if (len2 <= 0)
389: return crc1;
390:
391: /* put operator for one zero bit in odd */
392: odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
393: row = 1;
394: for (n = 1; n < GF2_DIM; n++) {
395: odd[n] = row;
396: row <<= 1;
397: }
398:
399: /* put operator for two zero bits in even */
400: gf2_matrix_square(even, odd);
401:
402: /* put operator for four zero bits in odd */
403: gf2_matrix_square(odd, even);
404:
405: /* apply len2 zeros to crc1 (first square will put the operator for one
406: zero byte, eight zero bits, in even) */
407: do {
408: /* apply zeros operator for this bit of len2 */
409: gf2_matrix_square(even, odd);
410: if (len2 & 1)
411: crc1 = gf2_matrix_times(even, crc1);
412: len2 >>= 1;
413:
414: /* if no more bits set, then done */
415: if (len2 == 0)
416: break;
417:
418: /* another iteration of the loop with odd and even swapped */
419: gf2_matrix_square(odd, even);
420: if (len2 & 1)
421: crc1 = gf2_matrix_times(odd, crc1);
422: len2 >>= 1;
423:
424: /* if no more bits set, then done */
425: } while (len2 != 0);
426:
427: /* return combined crc */
428: crc1 ^= crc2;
429: return crc1;
430: }
431:
432: /* ========================================================================= */
433: uLong ZEXPORT crc32_combine(crc1, crc2, len2)
434: uLong crc1;
435: uLong crc2;
436: z_off_t len2;
437: {
438: return crc32_combine_(crc1, crc2, len2);
439: }
440:
441: uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
442: uLong crc1;
443: uLong crc2;
444: z_off64_t len2;
445: {
446: return crc32_combine_(crc1, crc2, len2);
447: }
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