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(). */
37 # ifdef STDC /* need ANSI C limits.h to determine sizes */
40 # if (UINT_MAX == 0xffffffffUL)
41 typedef unsigned int u4;
43 # if (ULONG_MAX == 0xffffffffUL)
44 typedef unsigned long u4;
46 # if (USHRT_MAX == 0xffffffffUL)
47 typedef unsigned short u4;
49 # undef BYFOUR /* can't find a four-byte integer type! */
54 #endif /* !NOBYFOUR */
56 /* Definitions for doing the crc four data bytes at a time. */
58 typedef u4 crc_table_t;
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));
67 typedef unsigned long crc_table_t;
71 /* Local functions for crc concatenation */
72 local unsigned long gf2_matrix_times OF((unsigned long *mat,
74 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
75 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
78 #ifdef DYNAMIC_CRC_TABLE
80 local volatile int crc_table_empty = 1;
81 local crc_table_t FAR crc_table[TBLS][256];
82 local void make_crc_table OF((void));
84 local void write_table OF((FILE *, const crc_table_t FAR *));
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.
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.
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.
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.
112 local void make_crc_table()
116 crc_table_t poly; /* polynomial exclusive-or pattern */
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};
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) */
127 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
129 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
130 poly |= (crc_table_t)1 << (31 - p[n]);
132 /* generate a crc for every 8-bit value */
133 for (n = 0; n < 256; n++) {
135 for (k = 0; k < 8; k++)
136 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
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++) {
145 crc_table[4][n] = REV(c);
146 for (k = 1; k < 4; k++) {
147 c = crc_table[0][c & 0xff] ^ (c >> 8);
149 crc_table[k + 4][n] = REV(c);
156 else { /* not first */
157 /* wait for the other guy to finish (not efficient, but rare) */
158 while (crc_table_empty)
163 /* write out CRC tables to crc32.h */
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");
171 fprintf(out, "local const crc_table_t FAR ");
172 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
173 write_table(out, crc_table[0]);
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]);
180 fprintf(out, "#endif\n");
182 fprintf(out, " }\n};\n");
185 #endif /* MAKECRCH */
189 local void write_table(out, table)
191 const crc_table_t FAR *table;
195 for (n = 0; n < 256; n++)
196 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
197 (unsigned long)(table[n]),
198 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
200 #endif /* MAKECRCH */
202 #else /* !DYNAMIC_CRC_TABLE */
203 /* ========================================================================
204 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
207 #endif /* DYNAMIC_CRC_TABLE */
209 /* =========================================================================
210 * This function can be used by asm versions of crc32()
212 const unsigned long FAR * ZEXPORT get_crc_table()
214 #ifdef DYNAMIC_CRC_TABLE
217 #endif /* DYNAMIC_CRC_TABLE */
218 return (const unsigned long FAR *)crc_table;
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
225 /* ========================================================================= */
226 unsigned long ZEXPORT crc32(crc, buf, len)
228 const unsigned char FAR *buf;
231 if (buf == Z_NULL) return 0UL;
233 #ifdef DYNAMIC_CRC_TABLE
236 #endif /* DYNAMIC_CRC_TABLE */
239 if (sizeof(void *) == sizeof(ptrdiff_t)) {
243 if (*((unsigned char *)(&endian)))
244 return crc32_little(crc, buf, len);
246 return crc32_big(crc, buf, len);
249 crc = crc ^ 0xffffffffUL;
257 return crc ^ 0xffffffffUL;
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
268 /* ========================================================================= */
269 local unsigned long crc32_little(crc, buf, len)
271 const unsigned char FAR *buf;
275 register const u4 FAR *buf4;
279 while (len && ((ptrdiff_t)buf & 3)) {
280 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
284 buf4 = (const u4 FAR *)(const void FAR *)buf;
293 buf = (const unsigned char FAR *)buf4;
296 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
299 return (unsigned long)c;
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
308 /* ========================================================================= */
309 local unsigned long crc32_big(crc, buf, len)
311 const unsigned char FAR *buf;
315 register const u4 FAR *buf4;
319 while (len && ((ptrdiff_t)buf & 3)) {
320 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
324 buf4 = (const u4 FAR *)(const void FAR *)buf;
335 buf = (const unsigned char FAR *)buf4;
338 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
341 return (unsigned long)(REV(c));
346 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
348 /* ========================================================================= */
349 local unsigned long gf2_matrix_times(mat, vec)
365 /* ========================================================================= */
366 local void gf2_matrix_square(square, mat)
367 unsigned long *square;
372 for (n = 0; n < GF2_DIM; n++)
373 square[n] = gf2_matrix_times(mat, mat[n]);
376 /* ========================================================================= */
377 local uLong crc32_combine_(crc1, crc2, len2)
384 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
385 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
387 /* degenerate case (also disallow negative lengths) */
391 /* put operator for one zero bit in odd */
392 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
394 for (n = 1; n < GF2_DIM; n++) {
399 /* put operator for two zero bits in even */
400 gf2_matrix_square(even, odd);
402 /* put operator for four zero bits in odd */
403 gf2_matrix_square(odd, even);
405 /* apply len2 zeros to crc1 (first square will put the operator for one
406 zero byte, eight zero bits, in even) */
408 /* apply zeros operator for this bit of len2 */
409 gf2_matrix_square(even, odd);
411 crc1 = gf2_matrix_times(even, crc1);
414 /* if no more bits set, then done */
418 /* another iteration of the loop with odd and even swapped */
419 gf2_matrix_square(odd, even);
421 crc1 = gf2_matrix_times(odd, crc1);
424 /* if no more bits set, then done */
427 /* return combined crc */
432 /* ========================================================================= */
433 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
438 return crc32_combine_(crc1, crc2, len2);
441 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
446 return crc32_combine_(crc1, crc2, len2);