1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011, 2012 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 local unsigned long crc32_little OF((unsigned long,
63 const unsigned char FAR *, unsigned));
64 local unsigned long crc32_big OF((unsigned long,
65 const unsigned char FAR *, unsigned));
68 typedef unsigned long crc_table_t;
72 /* Local functions for crc concatenation */
73 local unsigned long gf2_matrix_times OF((unsigned long *mat,
75 local void gf2_matrix_square OF((unsigned long *square, unsigned long *mat));
76 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
79 #ifdef DYNAMIC_CRC_TABLE
81 local volatile int crc_table_empty = 1;
82 local crc_table_t FAR crc_table[TBLS][256];
83 local void make_crc_table OF((void));
85 local void write_table OF((FILE *, const crc_table_t FAR *));
88 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
89 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.
91 Polynomials over GF(2) are represented in binary, one bit per coefficient,
92 with the lowest powers in the most significant bit. Then adding polynomials
93 is just exclusive-or, and multiplying a polynomial by x is a right shift by
94 one. If we call the above polynomial p, and represent a byte as the
95 polynomial q, also with the lowest power in the most significant bit (so the
96 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
97 where a mod b means the remainder after dividing a by b.
99 This calculation is done using the shift-register method of multiplying and
100 taking the remainder. The register is initialized to zero, and for each
101 incoming bit, x^32 is added mod p to the register if the bit is a one (where
102 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
103 x (which is shifting right by one and adding x^32 mod p if the bit shifted
104 out is a one). We start with the highest power (least significant bit) of
105 q and repeat for all eight bits of q.
107 The first table is simply the CRC of all possible eight bit values. This is
108 all the information needed to generate CRCs on data a byte at a time for all
109 combinations of CRC register values and incoming bytes. The remaining tables
110 allow for word-at-a-time CRC calculation for both big-endian and little-
111 endian machines, where a word is four bytes.
113 local void make_crc_table()
117 crc_table_t poly; /* polynomial exclusive-or pattern */
118 /* terms of polynomial defining this crc (except x^32): */
119 static volatile int first = 1; /* flag to limit concurrent making */
120 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
122 /* See if another task is already doing this (not thread-safe, but better
123 than nothing -- significantly reduces duration of vulnerability in
124 case the advice about DYNAMIC_CRC_TABLE is ignored) */
128 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
130 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
131 poly |= (crc_table_t)1 << (31 - p[n]);
133 /* generate a crc for every 8-bit value */
134 for (n = 0; n < 256; n++) {
136 for (k = 0; k < 8; k++)
137 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
142 /* generate crc for each value followed by one, two, and three zeros,
143 and then the byte reversal of those as well as the first table */
144 for (n = 0; n < 256; n++) {
146 crc_table[4][n] = ZSWAP32(c);
147 for (k = 1; k < 4; k++) {
148 c = crc_table[0][c & 0xff] ^ (c >> 8);
150 crc_table[k + 4][n] = ZSWAP32(c);
157 else { /* not first */
158 /* wait for the other guy to finish (not efficient, but rare) */
159 while (crc_table_empty)
164 /* write out CRC tables to crc32.h */
168 out = fopen("crc32.h", "w");
169 if (out == NULL) return;
170 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
171 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
172 fprintf(out, "local const crc_table_t FAR ");
173 fprintf(out, "crc_table[TBLS][256] =\n{\n {\n");
174 write_table(out, crc_table[0]);
176 fprintf(out, "#ifdef BYFOUR\n");
177 for (k = 1; k < 8; k++) {
178 fprintf(out, " },\n {\n");
179 write_table(out, crc_table[k]);
181 fprintf(out, "#endif\n");
183 fprintf(out, " }\n};\n");
186 #endif /* MAKECRCH */
190 local void write_table(out, table)
192 const crc_table_t FAR *table;
196 for (n = 0; n < 256; n++)
197 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
198 (unsigned long)(table[n]),
199 n == 255 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
201 #endif /* MAKECRCH */
203 #else /* !DYNAMIC_CRC_TABLE */
204 /* ========================================================================
205 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
208 #endif /* DYNAMIC_CRC_TABLE */
210 /* =========================================================================
211 * This function can be used by asm versions of crc32()
213 const unsigned long FAR * ZEXPORT get_crc_table()
215 #ifdef DYNAMIC_CRC_TABLE
218 #endif /* DYNAMIC_CRC_TABLE */
219 return (const unsigned long FAR *)crc_table;
222 /* ========================================================================= */
223 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
224 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
226 /* ========================================================================= */
227 unsigned long ZEXPORT crc32(crc, buf, len)
229 const unsigned char FAR *buf;
232 if (buf == Z_NULL) return 0UL;
234 #ifdef DYNAMIC_CRC_TABLE
237 #endif /* DYNAMIC_CRC_TABLE */
240 if (sizeof(void *) == sizeof(ptrdiff_t)) {
244 if (*((unsigned char *)(&endian)))
245 return crc32_little(crc, buf, len);
247 return crc32_big(crc, buf, len);
250 crc = crc ^ 0xffffffffUL;
258 return crc ^ 0xffffffffUL;
263 /* ========================================================================= */
264 #define DOLIT4 c ^= *buf4++; \
265 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
266 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
267 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
269 /* ========================================================================= */
270 local unsigned long crc32_little(crc, buf, len)
272 const unsigned char FAR *buf;
276 register const u4 FAR *buf4;
280 while (len && ((ptrdiff_t)buf & 3)) {
281 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
285 buf4 = (const u4 FAR *)(const void FAR *)buf;
294 buf = (const unsigned char FAR *)buf4;
297 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
300 return (unsigned long)c;
303 /* ========================================================================= */
304 #define DOBIG4 c ^= *++buf4; \
305 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
306 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
307 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
309 /* ========================================================================= */
310 local unsigned long crc32_big(crc, buf, len)
312 const unsigned char FAR *buf;
316 register const u4 FAR *buf4;
318 c = ZSWAP32((u4)crc);
320 while (len && ((ptrdiff_t)buf & 3)) {
321 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
325 buf4 = (const u4 FAR *)(const void FAR *)buf;
336 buf = (const unsigned char FAR *)buf4;
339 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
342 return (unsigned long)(ZSWAP32(c));
347 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
349 /* ========================================================================= */
350 local unsigned long gf2_matrix_times(mat, vec)
366 /* ========================================================================= */
367 local void gf2_matrix_square(square, mat)
368 unsigned long *square;
373 for (n = 0; n < GF2_DIM; n++)
374 square[n] = gf2_matrix_times(mat, mat[n]);
377 /* ========================================================================= */
378 local uLong crc32_combine_(crc1, crc2, len2)
385 unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
386 unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
388 /* degenerate case (also disallow negative lengths) */
392 /* put operator for one zero bit in odd */
393 odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
395 for (n = 1; n < GF2_DIM; n++) {
400 /* put operator for two zero bits in even */
401 gf2_matrix_square(even, odd);
403 /* put operator for four zero bits in odd */
404 gf2_matrix_square(odd, even);
406 /* apply len2 zeros to crc1 (first square will put the operator for one
407 zero byte, eight zero bits, in even) */
409 /* apply zeros operator for this bit of len2 */
410 gf2_matrix_square(even, odd);
412 crc1 = gf2_matrix_times(even, crc1);
415 /* if no more bits set, then done */
419 /* another iteration of the loop with odd and even swapped */
420 gf2_matrix_square(odd, even);
422 crc1 = gf2_matrix_times(odd, crc1);
425 /* if no more bits set, then done */
428 /* return combined crc */
433 /* ========================================================================= */
434 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
439 return crc32_combine_(crc1, crc2, len2);
442 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
447 return crc32_combine_(crc1, crc2, len2);