1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
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.
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().
21 DYNAMIC_CRC_TABLE and MAKECRCH can be #defined to write out crc32.h.
26 # ifndef DYNAMIC_CRC_TABLE
27 # define DYNAMIC_CRC_TABLE
28 # endif /* !DYNAMIC_CRC_TABLE */
31 #include "zutil.h" /* for STDC and FAR definitions */
35 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
40 # ifdef STDC /* need ANSI C limits.h to determine sizes */
43 # if (UINT_MAX == 0xffffffffUL)
44 typedef unsigned int u4;
46 # if (ULONG_MAX == 0xffffffffUL)
47 typedef unsigned long u4;
49 # if (USHRT_MAX == 0xffffffffUL)
50 typedef unsigned short u4;
52 # undef BYFOUR /* can't find a four-byte integer type! */
57 #endif /* !NOBYFOUR */
59 /* Definitions for doing the crc four data bytes at a time. */
61 typedef u4 crc_table_t;
62 # define REV(w) ((((w)>>24)&0xff)+(((w)>>8)&0xff00)+ \
63 (((w)&0xff00)<<8)+(((w)&0xff)<<24))
64 local unsigned long crc32_little OF((unsigned long,
65 const unsigned char FAR *, unsigned));
66 local unsigned long crc32_big OF((unsigned long,
67 const unsigned char FAR *, unsigned));
70 typedef unsigned long crc_table_t;
74 /* Local functions for crc concatenation */
75 local unsigned long gf2_matrix_times OF((unsigned long *mat,
77 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
78 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
81 #ifdef DYNAMIC_CRC_TABLE
83 local volatile int crc_table_empty = 1;
84 local crc_table_t FAR crc_table[TBLS][256];
85 local void make_crc_table OF((void));
87 local void write_table OF((FILE *, const crc_table_t FAR *));
90 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
91 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.
93 Polynomials over GF(2) are represented in binary, one bit per coefficient,
94 with the lowest powers in the most significant bit. Then adding polynomials
95 is just exclusive-or, and multiplying a polynomial by x is a right shift by
96 one. If we call the above polynomial p, and represent a byte as the
97 polynomial q, also with the lowest power in the most significant bit (so the
98 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
99 where a mod b means the remainder after dividing a by b.
101 This calculation is done using the shift-register method of multiplying and
102 taking the remainder. The register is initialized to zero, and for each
103 incoming bit, x^32 is added mod p to the register if the bit is a one (where
104 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
105 x (which is shifting right by one and adding x^32 mod p if the bit shifted
106 out is a one). We start with the highest power (least significant bit) of
107 q and repeat for all eight bits of q.
109 The first table is simply the CRC of all possible eight bit values. This is
110 all the information needed to generate CRCs on data a byte at a time for all
111 combinations of CRC register values and incoming bytes. The remaining tables
112 allow for word-at-a-time CRC calculation for both big-endian and little-
113 endian machines, where a word is four bytes.
115 local void make_crc_table()
119 crc_table_t poly; /* polynomial exclusive-or pattern */
120 /* terms of polynomial defining this crc (except x^32): */
121 static volatile int first = 1; /* flag to limit concurrent making */
122 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
124 /* See if another task is already doing this (not thread-safe, but better
125 than nothing -- significantly reduces duration of vulnerability in
126 case the advice about DYNAMIC_CRC_TABLE is ignored) */
130 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
132 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
133 poly |= (crc_table_t)1 << (31 - p[n]);
135 /* generate a crc for every 8-bit value */
136 for (n = 0; n < 256; n++) {
138 for (k = 0; k < 8; k++)
139 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
144 /* generate crc for each value followed by one, two, and three zeros,
145 and then the byte reversal of those as well as the first table */
146 for (n = 0; n < 256; n++) {
148 crc_table[4][n] = REV(c);
149 for (k = 1; k < 4; k++) {
150 c = crc_table[0][c & 0xff] ^ (c >> 8);
152 crc_table[k + 4][n] = REV(c);
159 else { /* not first */
160 /* wait for the other guy to finish (not efficient, but rare) */
161 while (crc_table_empty)
166 /* write out CRC tables to crc32.h */
170 out = fopen("crc32.h", "w");
171 if (out == NULL) return;
172 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
173 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
174 fprintf(out, "local const crc_table_t FAR ");
175 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
176 write_table(out, crc_table[0]);
178 fprintf(out, "#ifdef BYFOUR\n");
179 for (k = 1; k < 8; k++) {
180 fprintf(out, " },\n {\n");
181 write_table(out, crc_table[k]);
183 fprintf(out, "#endif\n");
185 fprintf(out, " }\n};\n");
188 #endif /* MAKECRCH */
192 local void write_table(out, table)
194 const crc_table_t FAR *table;
198 for (n = 0; n < 256; n++)
199 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
200 (unsigned long)(table[n]),
201 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
203 #endif /* MAKECRCH */
205 #else /* !DYNAMIC_CRC_TABLE */
206 /* ========================================================================
207 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
210 #endif /* DYNAMIC_CRC_TABLE */
212 /* =========================================================================
213 * This function can be used by asm versions of crc32()
215 const unsigned long FAR * ZEXPORT get_crc_table()
217 #ifdef DYNAMIC_CRC_TABLE
220 #endif /* DYNAMIC_CRC_TABLE */
221 return (const unsigned long FAR *)crc_table;
224 /* ========================================================================= */
225 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
226 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
228 /* ========================================================================= */
229 unsigned long ZEXPORT crc32(crc, buf, len)
231 const unsigned char FAR *buf;
234 if (buf == Z_NULL) return 0UL;
236 #ifdef DYNAMIC_CRC_TABLE
239 #endif /* DYNAMIC_CRC_TABLE */
242 if (sizeof(void *) == sizeof(ptrdiff_t)) {
246 if (*((unsigned char *)(&endian)))
247 return crc32_little(crc, buf, len);
249 return crc32_big(crc, buf, len);
252 crc = crc ^ 0xffffffffUL;
260 return crc ^ 0xffffffffUL;
265 /* ========================================================================= */
266 #define DOLIT4 c ^= *buf4++; \
267 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
268 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
269 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
271 /* ========================================================================= */
272 local unsigned long crc32_little(crc, buf, len)
274 const unsigned char FAR *buf;
278 register const u4 FAR *buf4;
282 while (len && ((ptrdiff_t)buf & 3)) {
283 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
287 buf4 = (const u4 FAR *)(const void FAR *)buf;
296 buf = (const unsigned char FAR *)buf4;
299 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
302 return (unsigned long)c;
305 /* ========================================================================= */
306 #define DOBIG4 c ^= *++buf4; \
307 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
308 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
309 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
311 /* ========================================================================= */
312 local unsigned long crc32_big(crc, buf, len)
314 const unsigned char FAR *buf;
318 register const u4 FAR *buf4;
322 while (len && ((ptrdiff_t)buf & 3)) {
323 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
327 buf4 = (const u4 FAR *)(const void FAR *)buf;
338 buf = (const unsigned char FAR *)buf4;
341 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
344 return (unsigned long)(REV(c));
349 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
351 /* ========================================================================= */
352 local unsigned long gf2_matrix_times(mat, vec)
368 /* ========================================================================= */
369 local void gf2_matrix_square(square, mat)
370 unsigned long *square;
375 for (n = 0; n < GF2_DIM; n++)
376 square[n] = gf2_matrix_times(mat, mat[n]);
379 /* ========================================================================= */
380 local uLong crc32_combine_(crc1, crc2, len2)
387 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
388 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
390 /* degenerate case (also disallow negative lengths) */
394 /* put operator for one zero bit in odd */
395 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
397 for (n = 1; n < GF2_DIM; n++) {
402 /* put operator for two zero bits in even */
403 gf2_matrix_square(even, odd);
405 /* put operator for four zero bits in odd */
406 gf2_matrix_square(odd, even);
408 /* apply len2 zeros to crc1 (first square will put the operator for one
409 zero byte, eight zero bits, in even) */
411 /* apply zeros operator for this bit of len2 */
412 gf2_matrix_square(even, odd);
414 crc1 = gf2_matrix_times(even, crc1);
417 /* if no more bits set, then done */
421 /* another iteration of the loop with odd and even swapped */
422 gf2_matrix_square(odd, even);
424 crc1 = gf2_matrix_times(odd, crc1);
427 /* if no more bits set, then done */
430 /* return combined crc */
435 /* ========================================================================= */
436 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
441 return crc32_combine_(crc1, crc2, len2);
444 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
449 return crc32_combine_(crc1, crc2, len2);