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)+(((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 #ifdef _LARGEFILE64_SOURCE
72 local uLong
crc32_combine_(uLong crc1
, uLong crc2
, off64_t len2
);
74 local uLong
crc32_combine_(uLong crc1
, uLong crc2
, z_off_t len2
);
78 #ifdef DYNAMIC_CRC_TABLE
80 local
volatile int crc_table_empty
= 1;
81 local
unsigned long FAR crc_table
[TBLS
][256];
82 local
void make_crc_table
OF((void));
84 local
void write_table
OF((FILE *, const unsigned long 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 unsigned long 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
< sizeof(p
)/sizeof(unsigned char); n
++)
130 poly
|= 1UL << (31 - p
[n
]);
132 /* generate a crc for every 8-bit value */
133 for (n
= 0; n
< 256; n
++) {
134 c
= (unsigned long)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 unsigned long 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 unsigned long FAR
*table
;
195 for (n
= 0; n
< 256; n
++)
196 fprintf(out
, "%s0x%08lxUL%s", n
% 5 ? "" : " ", table
[n
],
197 n
== 255 ? "\n" : (n
% 5 == 4 ? ",\n" : ", "));
199 #endif /* MAKECRCH */
201 #else /* !DYNAMIC_CRC_TABLE */
202 /* ========================================================================
203 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
206 #endif /* DYNAMIC_CRC_TABLE */
208 /* =========================================================================
209 * This function can be used by asm versions of crc32()
211 const unsigned long FAR
* ZEXPORT
get_crc_table()
213 #ifdef DYNAMIC_CRC_TABLE
216 #endif /* DYNAMIC_CRC_TABLE */
217 return (const unsigned long FAR
*)crc_table
;
220 /* ========================================================================= */
221 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
222 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
224 /* ========================================================================= */
225 unsigned long ZEXPORT
crc32(crc
, buf
, len
)
227 const unsigned char FAR
*buf
;
230 if (buf
== Z_NULL
) return 0UL;
232 #ifdef DYNAMIC_CRC_TABLE
235 #endif /* DYNAMIC_CRC_TABLE */
238 if (sizeof(void *) == sizeof(ptrdiff_t)) {
242 if (*((unsigned char *)(&endian
)))
243 return crc32_little(crc
, buf
, len
);
245 return crc32_big(crc
, buf
, len
);
248 crc
= crc
^ 0xffffffffUL
;
256 return crc
^ 0xffffffffUL
;
261 /* ========================================================================= */
262 #define DOLIT4 c ^= *buf4++; \
263 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
264 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
265 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
267 /* ========================================================================= */
268 local
unsigned long crc32_little(crc
, buf
, len
)
270 const unsigned char FAR
*buf
;
274 register const u4 FAR
*buf4
;
278 while (len
&& ((ptrdiff_t)buf
& 3)) {
279 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
283 buf4
= (const u4 FAR
*)(const void FAR
*)buf
;
292 buf
= (const unsigned char FAR
*)buf4
;
295 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
298 return (unsigned long)c
;
301 /* ========================================================================= */
302 #define DOBIG4 c ^= *++buf4; \
303 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
304 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
305 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
307 /* ========================================================================= */
308 local
unsigned long crc32_big(crc
, buf
, len
)
310 const unsigned char FAR
*buf
;
314 register const u4 FAR
*buf4
;
318 while (len
&& ((ptrdiff_t)buf
& 3)) {
319 c
= crc_table
[4][(c
>> 24) ^ *buf
++] ^ (c
<< 8);
323 buf4
= (const u4 FAR
*)(const void FAR
*)buf
;
334 buf
= (const unsigned char FAR
*)buf4
;
337 c
= crc_table
[4][(c
>> 24) ^ *buf
++] ^ (c
<< 8);
340 return (unsigned long)(REV(c
));
345 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
347 /* ========================================================================= */
348 local
unsigned long gf2_matrix_times(mat
, vec
)
364 /* ========================================================================= */
365 local
void gf2_matrix_square(square
, mat
)
366 unsigned long *square
;
371 for (n
= 0; n
< GF2_DIM
; n
++)
372 square
[n
] = gf2_matrix_times(mat
, mat
[n
]);
375 /* ========================================================================= */
376 local uLong
crc32_combine_(crc1
, crc2
, len2
)
379 #ifdef _LARGEFILE64_SOURCE
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 */
394 /* put operator for one zero bit in odd */
395 odd
[0] = 0xedb88320L
; /* 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 #ifdef _LARGEFILE64_SOURCE
445 uLong ZEXPORT
crc32_combine64(crc1
, crc2
, len2
)
450 return crc32_combine_(crc1
, crc2
, len2
);
453 uLong ZEXPORT
crc32_combine64(crc1
, crc2
, len2
)
458 return crc32_combine_(crc1
, crc2
, len2
);