1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006 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)&0xff)+(((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
));
71 local uLong
crc32_combine_(uLong crc1
, uLong crc2
, z_off64_t len2
);
74 #ifdef DYNAMIC_CRC_TABLE
76 local
volatile int crc_table_empty
= 1;
77 local
unsigned long FAR crc_table
[TBLS
][256];
78 local
void make_crc_table
OF((void));
80 local
void write_table
OF((FILE *, const unsigned long FAR
*));
83 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
84 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.
86 Polynomials over GF(2) are represented in binary, one bit per coefficient,
87 with the lowest powers in the most significant bit. Then adding polynomials
88 is just exclusive-or, and multiplying a polynomial by x is a right shift by
89 one. If we call the above polynomial p, and represent a byte as the
90 polynomial q, also with the lowest power in the most significant bit (so the
91 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
92 where a mod b means the remainder after dividing a by b.
94 This calculation is done using the shift-register method of multiplying and
95 taking the remainder. The register is initialized to zero, and for each
96 incoming bit, x^32 is added mod p to the register if the bit is a one (where
97 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
98 x (which is shifting right by one and adding x^32 mod p if the bit shifted
99 out is a one). We start with the highest power (least significant bit) of
100 q and repeat for all eight bits of q.
102 The first table is simply the CRC of all possible eight bit values. This is
103 all the information needed to generate CRCs on data a byte at a time for all
104 combinations of CRC register values and incoming bytes. The remaining tables
105 allow for word-at-a-time CRC calculation for both big-endian and little-
106 endian machines, where a word is four bytes.
108 local
void make_crc_table()
112 unsigned long poly
; /* polynomial exclusive-or pattern */
113 /* terms of polynomial defining this crc (except x^32): */
114 static volatile int first
= 1; /* flag to limit concurrent making */
115 static const unsigned char p
[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
117 /* See if another task is already doing this (not thread-safe, but better
118 than nothing -- significantly reduces duration of vulnerability in
119 case the advice about DYNAMIC_CRC_TABLE is ignored) */
123 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
125 for (n
= 0; n
< sizeof(p
)/sizeof(unsigned char); n
++)
126 poly
|= 1UL << (31 - p
[n
]);
128 /* generate a crc for every 8-bit value */
129 for (n
= 0; n
< 256; n
++) {
130 c
= (unsigned long)n
;
131 for (k
= 0; k
< 8; k
++)
132 c
= c
& 1 ? poly
^ (c
>> 1) : c
>> 1;
137 /* generate crc for each value followed by one, two, and three zeros,
138 and then the byte reversal of those as well as the first table */
139 for (n
= 0; n
< 256; n
++) {
141 crc_table
[4][n
] = REV(c
);
142 for (k
= 1; k
< 4; k
++) {
143 c
= crc_table
[0][c
& 0xff] ^ (c
>> 8);
145 crc_table
[k
+ 4][n
] = REV(c
);
152 else { /* not first */
153 /* wait for the other guy to finish (not efficient, but rare) */
154 while (crc_table_empty
)
159 /* write out CRC tables to crc32.h */
163 out
= fopen("crc32.h", "w");
164 if (out
== NULL
) return;
165 fprintf(out
, "/* crc32.h -- tables for rapid CRC calculation\n");
166 fprintf(out
, " * Generated automatically by crc32.c\n */\n\n");
167 fprintf(out
, "local const unsigned long FAR ");
168 fprintf(out
, "crc_table[TBLS][256] =\n{\n {\n");
169 write_table(out
, crc_table
[0]);
171 fprintf(out
, "#ifdef BYFOUR\n");
172 for (k
= 1; k
< 8; k
++) {
173 fprintf(out
, " },\n {\n");
174 write_table(out
, crc_table
[k
]);
176 fprintf(out
, "#endif\n");
178 fprintf(out
, " }\n};\n");
181 #endif /* MAKECRCH */
185 local
void write_table(out
, table
)
187 const unsigned long FAR
*table
;
191 for (n
= 0; n
< 256; n
++)
192 fprintf(out
, "%s0x%08lxUL%s", n
% 5 ? "" : " ", table
[n
],
193 n
== 255 ? "\n" : (n
% 5 == 4 ? ",\n" : ", "));
195 #endif /* MAKECRCH */
197 #else /* !DYNAMIC_CRC_TABLE */
198 /* ========================================================================
199 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
202 #endif /* DYNAMIC_CRC_TABLE */
204 /* =========================================================================
205 * This function can be used by asm versions of crc32()
207 const uLong FAR
* ZEXPORT
get_crc_table()
209 #ifdef DYNAMIC_CRC_TABLE
212 #endif /* DYNAMIC_CRC_TABLE */
213 return (const uLong FAR
*)crc_table
;
216 /* ========================================================================= */
217 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
218 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
220 /* ========================================================================= */
221 uLong ZEXPORT
crc32(crc
, buf
, len
)
226 if (buf
== Z_NULL
) return 0UL;
228 #ifdef DYNAMIC_CRC_TABLE
231 #endif /* DYNAMIC_CRC_TABLE */
234 if (sizeof(void *) == sizeof(ptrdiff_t)) {
238 if (*((unsigned char *)(&endian
)))
239 return crc32_little(crc
, buf
, len
);
241 return crc32_big(crc
, buf
, len
);
244 crc
= crc
^ 0xffffffffUL
;
252 return crc
^ 0xffffffffUL
;
257 /* ========================================================================= */
258 #define DOLIT4 c ^= *buf4++; \
259 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
260 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
261 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
263 /* ========================================================================= */
264 local
unsigned long crc32_little(crc
, buf
, len
)
266 const unsigned char FAR
*buf
;
270 register const u4 FAR
*buf4
;
274 while (len
&& ((ptrdiff_t)buf
& 3)) {
275 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
279 buf4
= (const u4 FAR
*)(const void FAR
*)buf
;
288 buf
= (const unsigned char FAR
*)buf4
;
291 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
294 return (unsigned long)c
;
297 /* ========================================================================= */
298 #define DOBIG4 c ^= *++buf4; \
299 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
300 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
301 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
303 /* ========================================================================= */
304 local
unsigned long crc32_big(crc
, buf
, len
)
306 const unsigned char FAR
*buf
;
310 register const u4 FAR
*buf4
;
314 while (len
&& ((ptrdiff_t)buf
& 3)) {
315 c
= crc_table
[4][(c
>> 24) ^ *buf
++] ^ (c
<< 8);
319 buf4
= (const u4 FAR
*)(const void FAR
*)buf
;
330 buf
= (const unsigned char FAR
*)buf4
;
333 c
= crc_table
[4][(c
>> 24) ^ *buf
++] ^ (c
<< 8);
336 return (unsigned long)(REV(c
));
341 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
343 /* ========================================================================= */
344 local
unsigned long gf2_matrix_times(mat
, vec
)
360 /* ========================================================================= */
361 local
void gf2_matrix_square(square
, mat
)
362 unsigned long *square
;
367 for (n
= 0; n
< GF2_DIM
; n
++)
368 square
[n
] = gf2_matrix_times(mat
, mat
[n
]);
371 /* ========================================================================= */
372 local uLong
crc32_combine_(crc1
, crc2
, len2
)
379 unsigned long even
[GF2_DIM
]; /* even-power-of-two zeros operator */
380 unsigned long odd
[GF2_DIM
]; /* odd-power-of-two zeros operator */
382 /* degenerate case (also disallow negative lengths) */
386 /* put operator for one zero bit in odd */
387 odd
[0] = 0xedb88320UL
; /* CRC-32 polynomial */
389 for (n
= 1; n
< GF2_DIM
; n
++) {
394 /* put operator for two zero bits in even */
395 gf2_matrix_square(even
, odd
);
397 /* put operator for four zero bits in odd */
398 gf2_matrix_square(odd
, even
);
400 /* apply len2 zeros to crc1 (first square will put the operator for one
401 zero byte, eight zero bits, in even) */
403 /* apply zeros operator for this bit of len2 */
404 gf2_matrix_square(even
, odd
);
406 crc1
= gf2_matrix_times(even
, crc1
);
409 /* if no more bits set, then done */
413 /* another iteration of the loop with odd and even swapped */
414 gf2_matrix_square(odd
, even
);
416 crc1
= gf2_matrix_times(odd
, crc1
);
419 /* if no more bits set, then done */
422 /* return combined crc */
427 /* ========================================================================= */
428 uLong ZEXPORT
crc32_combine(crc1
, crc2
, len2
)
433 return crc32_combine_(crc1
, crc2
, len2
);
436 uLong ZEXPORT
crc32_combine64(crc1
, crc2
, len2
)
441 return crc32_combine_(crc1
, crc2
, len2
);