1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 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 */
33 /* Definitions for doing the crc four data bytes at a time. */
34 #if !defined(NOBYFOUR) && defined(Z_U4)
38 local
unsigned long crc32_little
OF((unsigned long,
39 const unsigned char FAR
*, z_size_t
));
40 local
unsigned long crc32_big
OF((unsigned long,
41 const unsigned char FAR
*, z_size_t
));
47 /* Local functions for crc concatenation */
48 local
unsigned long gf2_matrix_times
OF((unsigned long *mat
,
50 local
void gf2_matrix_square
OF((unsigned long *square
, unsigned long *mat
));
51 local uLong crc32_combine_
OF((uLong crc1
, uLong crc2
, z_off64_t len2
));
54 #ifdef DYNAMIC_CRC_TABLE
56 local
volatile int crc_table_empty
= 1;
57 local z_crc_t FAR crc_table
[TBLS
][256];
58 local
void make_crc_table
OF((void));
60 local
void write_table
OF((FILE *, const z_crc_t FAR
*));
63 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
64 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.
66 Polynomials over GF(2) are represented in binary, one bit per coefficient,
67 with the lowest powers in the most significant bit. Then adding polynomials
68 is just exclusive-or, and multiplying a polynomial by x is a right shift by
69 one. If we call the above polynomial p, and represent a byte as the
70 polynomial q, also with the lowest power in the most significant bit (so the
71 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
72 where a mod b means the remainder after dividing a by b.
74 This calculation is done using the shift-register method of multiplying and
75 taking the remainder. The register is initialized to zero, and for each
76 incoming bit, x^32 is added mod p to the register if the bit is a one (where
77 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
78 x (which is shifting right by one and adding x^32 mod p if the bit shifted
79 out is a one). We start with the highest power (least significant bit) of
80 q and repeat for all eight bits of q.
82 The first table is simply the CRC of all possible eight bit values. This is
83 all the information needed to generate CRCs on data a byte at a time for all
84 combinations of CRC register values and incoming bytes. The remaining tables
85 allow for word-at-a-time CRC calculation for both big-endian and little-
86 endian machines, where a word is four bytes.
88 local
void make_crc_table()
92 z_crc_t poly
; /* polynomial exclusive-or pattern */
93 /* terms of polynomial defining this crc (except x^32): */
94 static volatile int first
= 1; /* flag to limit concurrent making */
95 static const unsigned char p
[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
97 /* See if another task is already doing this (not thread-safe, but better
98 than nothing -- significantly reduces duration of vulnerability in
99 case the advice about DYNAMIC_CRC_TABLE is ignored) */
103 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
105 for (n
= 0; n
< (int)(sizeof(p
)/sizeof(unsigned char)); n
++)
106 poly
|= (z_crc_t
)1 << (31 - p
[n
]);
108 /* generate a crc for every 8-bit value */
109 for (n
= 0; n
< 256; n
++) {
111 for (k
= 0; k
< 8; k
++)
112 c
= c
& 1 ? poly
^ (c
>> 1) : c
>> 1;
117 /* generate crc for each value followed by one, two, and three zeros,
118 and then the byte reversal of those as well as the first table */
119 for (n
= 0; n
< 256; n
++) {
121 crc_table
[4][n
] = ZSWAP32(c
);
122 for (k
= 1; k
< 4; k
++) {
123 c
= crc_table
[0][c
& 0xff] ^ (c
>> 8);
125 crc_table
[k
+ 4][n
] = ZSWAP32(c
);
132 else { /* not first */
133 /* wait for the other guy to finish (not efficient, but rare) */
134 while (crc_table_empty
)
139 /* write out CRC tables to crc32.h */
143 out
= fopen("crc32.h", "w");
144 if (out
== NULL
) return;
145 fprintf(out
, "/* crc32.h -- tables for rapid CRC calculation\n");
146 fprintf(out
, " * Generated automatically by crc32.c\n */\n\n");
147 fprintf(out
, "local const z_crc_t FAR ");
148 fprintf(out
, "crc_table[TBLS][256] =\n{\n {\n");
149 write_table(out
, crc_table
[0]);
151 fprintf(out
, "#ifdef BYFOUR\n");
152 for (k
= 1; k
< 8; k
++) {
153 fprintf(out
, " },\n {\n");
154 write_table(out
, crc_table
[k
]);
156 fprintf(out
, "#endif\n");
158 fprintf(out
, " }\n};\n");
161 #endif /* MAKECRCH */
165 local
void write_table(out
, table
)
167 const z_crc_t FAR
*table
;
171 for (n
= 0; n
< 256; n
++)
172 fprintf(out
, "%s0x%08lxUL%s", n
% 5 ? "" : " ",
173 (unsigned long)(table
[n
]),
174 n
== 255 ? "\n" : (n
% 5 == 4 ? ",\n" : ", "));
176 #endif /* MAKECRCH */
178 #else /* !DYNAMIC_CRC_TABLE */
179 /* ========================================================================
180 * Tables of CRC-32s of all single-byte values, made by make_crc_table().
183 #endif /* DYNAMIC_CRC_TABLE */
185 /* =========================================================================
186 * This function can be used by asm versions of crc32()
188 const z_crc_t FAR
* ZEXPORT
get_crc_table()
190 #ifdef DYNAMIC_CRC_TABLE
193 #endif /* DYNAMIC_CRC_TABLE */
194 return (const z_crc_t FAR
*)crc_table
;
197 /* ========================================================================= */
198 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
199 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
201 /* ========================================================================= */
202 unsigned long ZEXPORT
crc32_z(crc
, buf
, len
)
204 const unsigned char FAR
*buf
;
207 if (buf
== Z_NULL
) return 0UL;
209 #ifdef DYNAMIC_CRC_TABLE
212 #endif /* DYNAMIC_CRC_TABLE */
215 if (sizeof(void *) == sizeof(ptrdiff_t)) {
219 if (*((unsigned char *)(&endian
)))
220 return crc32_little(crc
, buf
, len
);
222 return crc32_big(crc
, buf
, len
);
225 crc
= crc
^ 0xffffffffUL
;
233 return crc
^ 0xffffffffUL
;
236 /* ========================================================================= */
237 unsigned long ZEXPORT
crc32(crc
, buf
, len
)
239 const unsigned char FAR
*buf
;
242 return crc32_z(crc
, buf
, len
);
248 This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit
249 integer pointer type. This violates the strict aliasing rule, where a
250 compiler can assume, for optimization purposes, that two pointers to
251 fundamentally different types won't ever point to the same memory. This can
252 manifest as a problem only if one of the pointers is written to. This code
253 only reads from those pointers. So long as this code remains isolated in
254 this compilation unit, there won't be a problem. For this reason, this code
255 should not be copied and pasted into a compilation unit in which other code
256 writes to the buffer that is passed to these routines.
259 /* ========================================================================= */
260 #define DOLIT4 c ^= *buf4++; \
261 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
262 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
263 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
265 /* ========================================================================= */
266 local
unsigned long crc32_little(crc
, buf
, len
)
268 const unsigned char FAR
*buf
;
272 register const z_crc_t FAR
*buf4
;
276 while (len
&& ((ptrdiff_t)buf
& 3)) {
277 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
281 buf4
= (const z_crc_t FAR
*)(const void FAR
*)buf
;
290 buf
= (const unsigned char FAR
*)buf4
;
293 c
= crc_table
[0][(c
^ *buf
++) & 0xff] ^ (c
>> 8);
296 return (unsigned long)c
;
299 /* ========================================================================= */
300 #define DOBIG4 c ^= *buf4++; \
301 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
302 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
303 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
305 /* ========================================================================= */
306 local
unsigned long crc32_big(crc
, buf
, len
)
308 const unsigned char FAR
*buf
;
312 register const z_crc_t FAR
*buf4
;
314 c
= ZSWAP32((z_crc_t
)crc
);
316 while (len
&& ((ptrdiff_t)buf
& 3)) {
317 c
= crc_table
[4][(c
>> 24) ^ *buf
++] ^ (c
<< 8);
321 buf4
= (const z_crc_t 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)(ZSWAP32(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
);