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
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().
24 # ifndef DYNAMIC_CRC_TABLE
25 # define DYNAMIC_CRC_TABLE
26 # endif /* !DYNAMIC_CRC_TABLE */
29 #include "zutil.h" /* for STDC and FAR definitions */
33 /* Find a four-byte integer type for crc32_little() and crc32_big(). */
35 # ifdef STDC /* need ANSI C limits.h to determine sizes */
38 # if (UINT_MAX == 0xffffffffUL)
39 typedef unsigned int u4;
41 # if (ULONG_MAX == 0xffffffffUL)
42 typedef unsigned long u4;
44 # if (USHRT_MAX == 0xffffffffUL)
45 typedef unsigned short u4;
47 # undef BYFOUR /* can't find a four-byte integer type! */
52 #endif /* !NOBYFOUR */
54 /* Definitions for doing the crc four data bytes at a time. */
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));
67 /* Local functions for crc concatenation */
68 local unsigned long gf2_matrix_times OF((unsigned long *mat,
70 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
72 #ifdef DYNAMIC_CRC_TABLE
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));
78 local void write_table OF((FILE *, const unsigned long FAR *));
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.
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.
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.
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.
106 local void make_crc_table()
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};
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) */
121 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
123 for (n = 0; n < sizeof(p)/sizeof(unsigned char); n++)
124 poly |= 1UL << (31 - p[n]);
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;
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++) {
139 crc_table[4][n] = REV(c);
140 for (k = 1; k < 4; k++) {
141 c = crc_table[0][c & 0xff] ^ (c >> 8);
143 crc_table[k + 4][n] = REV(c);
150 else { /* not first */
151 /* wait for the other guy to finish (not efficient, but rare) */
152 while (crc_table_empty)
157 /* write out CRC tables to crc32.h */
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]);
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]);
174 fprintf(out, "#endif\n");
176 fprintf(out, " }\n};\n");
179 #endif /* MAKECRCH */
183 local void write_table(out, table)
185 const unsigned long FAR *table;
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" : ", "));
193 #endif /* MAKECRCH */
195 #else /* !DYNAMIC_CRC_TABLE */
196 /* ========================================================================
197 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
200 #endif /* DYNAMIC_CRC_TABLE */
202 /* =========================================================================
203 * This function can be used by asm versions of crc32()
205 const unsigned long FAR * ZEXPORT get_crc_table()
207 #ifdef DYNAMIC_CRC_TABLE
210 #endif /* DYNAMIC_CRC_TABLE */
211 return (const unsigned long FAR *)crc_table;
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
218 /* ========================================================================= */
219 unsigned long ZEXPORT crc32(crc, buf, len)
221 const unsigned char FAR *buf;
224 if (buf == Z_NULL) return 0UL;
226 #ifdef DYNAMIC_CRC_TABLE
229 #endif /* DYNAMIC_CRC_TABLE */
232 if (sizeof(void *) == sizeof(ptrdiff_t)) {
236 if (*((unsigned char *)(&endian)))
237 return crc32_little(crc, buf, len);
239 return crc32_big(crc, buf, len);
242 crc = crc ^ 0xffffffffUL;
250 return crc ^ 0xffffffffUL;
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
261 /* ========================================================================= */
262 local unsigned long crc32_little(crc, buf, len)
264 const unsigned char FAR *buf;
268 register const u4 FAR *buf4;
272 while (len && ((ptrdiff_t)buf & 3)) {
273 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
277 buf4 = (const u4 FAR *)(const void FAR *)buf;
286 buf = (const unsigned char FAR *)buf4;
289 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
292 return (unsigned long)c;
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
301 /* ========================================================================= */
302 local unsigned long crc32_big(crc, buf, len)
304 const unsigned char FAR *buf;
308 register const u4 FAR *buf4;
312 while (len && ((ptrdiff_t)buf & 3)) {
313 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
317 buf4 = (const u4 FAR *)(const void FAR *)buf;
328 buf = (const unsigned char FAR *)buf4;
331 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
334 return (unsigned long)(REV(c));
339 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
341 /* ========================================================================= */
342 local unsigned long gf2_matrix_times(mat, vec)
358 /* ========================================================================= */
359 local void gf2_matrix_square(square, mat)
360 unsigned long *square;
365 for (n = 0; n < GF2_DIM; n++)
366 square[n] = gf2_matrix_times(mat, mat[n]);
369 /* ========================================================================= */
370 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
377 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
378 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
380 /* degenerate case */
384 /* put operator for one zero bit in odd */
385 odd[0] = 0xedb88320L; /* CRC-32 polynomial */
387 for (n = 1; n < GF2_DIM; n++) {
392 /* put operator for two zero bits in even */
393 gf2_matrix_square(even, odd);
395 /* put operator for four zero bits in odd */
396 gf2_matrix_square(odd, even);
398 /* apply len2 zeros to crc1 (first square will put the operator for one
399 zero byte, eight zero bits, in even) */
401 /* apply zeros operator for this bit of len2 */
402 gf2_matrix_square(even, odd);
404 crc1 = gf2_matrix_times(even, crc1);
407 /* if no more bits set, then done */
411 /* another iteration of the loop with odd and even swapped */
412 gf2_matrix_square(odd, even);
414 crc1 = gf2_matrix_times(odd, crc1);
417 /* if no more bits set, then done */
420 /* return combined crc */