1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2006, 2010, 2011, 2012, 2016, 2018 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. A main()
22 routine is also produced, so that this one source file can be compiled to an
28 # ifndef DYNAMIC_CRC_TABLE
29 # define DYNAMIC_CRC_TABLE
30 # endif /* !DYNAMIC_CRC_TABLE */
33 #include "zutil.h" /* for STDC and FAR definitions */
35 /* Definitions for doing the crc four data bytes at a time. */
36 #if !defined(NOBYFOUR) && defined(Z_U4)
40 local unsigned long crc32_little OF((unsigned long,
41 const unsigned char FAR *, z_size_t));
42 local unsigned long crc32_big OF((unsigned long,
43 const unsigned char FAR *, z_size_t));
49 /* Local functions for crc concatenation */
50 #define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
51 local z_crc_t gf2_matrix_times OF((const z_crc_t *mat, z_crc_t vec));
52 local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
53 local void crc32_combine_gen_ OF((z_crc_t *op, z_off64_t len2));
55 /* ========================================================================= */
56 local z_crc_t gf2_matrix_times(mat, vec)
73 #ifdef DYNAMIC_CRC_TABLE
75 local volatile int crc_table_empty = 1;
76 local z_crc_t FAR crc_table[TBLS][256];
77 local z_crc_t FAR crc_comb[GF2_DIM][GF2_DIM];
78 local void make_crc_table OF((void));
79 local void gf2_matrix_square OF((z_crc_t *square, const z_crc_t *mat));
81 local void write_table OF((FILE *, const z_crc_t FAR *, int));
84 /* ========================================================================= */
85 local void gf2_matrix_square(square, mat)
91 for (n = 0; n < GF2_DIM; n++)
92 square[n] = gf2_matrix_times(mat, mat[n]);
96 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
97 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.
99 Polynomials over GF(2) are represented in binary, one bit per coefficient,
100 with the lowest powers in the most significant bit. Then adding polynomials
101 is just exclusive-or, and multiplying a polynomial by x is a right shift by
102 one. If we call the above polynomial p, and represent a byte as the
103 polynomial q, also with the lowest power in the most significant bit (so the
104 byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
105 where a mod b means the remainder after dividing a by b.
107 This calculation is done using the shift-register method of multiplying and
108 taking the remainder. The register is initialized to zero, and for each
109 incoming bit, x^32 is added mod p to the register if the bit is a one (where
110 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
111 x (which is shifting right by one and adding x^32 mod p if the bit shifted
112 out is a one). We start with the highest power (least significant bit) of
113 q and repeat for all eight bits of q.
115 The first table is simply the CRC of all possible eight bit values. This is
116 all the information needed to generate CRCs on data a byte at a time for all
117 combinations of CRC register values and incoming bytes. The remaining tables
118 allow for word-at-a-time CRC calculation for both big-endian and little-
119 endian machines, where a word is four bytes.
121 local void make_crc_table()
125 z_crc_t poly; /* polynomial exclusive-or pattern */
126 /* terms of polynomial defining this crc (except x^32): */
127 static volatile int first = 1; /* flag to limit concurrent making */
128 static const unsigned char p[] = {0,1,2,4,5,7,8,10,11,12,16,22,23,26};
130 /* See if another task is already doing this (not thread-safe, but better
131 than nothing -- significantly reduces duration of vulnerability in
132 case the advice about DYNAMIC_CRC_TABLE is ignored) */
136 /* make exclusive-or pattern from polynomial (0xedb88320UL) */
138 for (n = 0; n < (int)(sizeof(p)/sizeof(unsigned char)); n++)
139 poly |= (z_crc_t)1 << (31 - p[n]);
141 /* generate a crc for every 8-bit value */
142 for (n = 0; n < 256; n++) {
144 for (k = 0; k < 8; k++)
145 c = c & 1 ? poly ^ (c >> 1) : c >> 1;
150 /* generate crc for each value followed by one, two, and three zeros,
151 and then the byte reversal of those as well as the first table */
152 for (n = 0; n < 256; n++) {
154 crc_table[4][n] = ZSWAP32(c);
155 for (k = 1; k < 4; k++) {
156 c = crc_table[0][c & 0xff] ^ (c >> 8);
158 crc_table[k + 4][n] = ZSWAP32(c);
163 /* generate zero operators table for crc32_combine() */
165 /* generate the operator to apply a single zero bit to a CRC -- the
166 first row adds the polynomial if the low bit is a 1, and the
167 remaining rows shift the CRC right one bit */
169 crc_comb[k][0] = 0xedb88320UL; /* CRC-32 polynomial */
171 for (n = 1; n < GF2_DIM; n++) {
172 crc_comb[k][n] = row;
176 /* generate operators that apply 2, 4, and 8 zeros to a CRC, putting
177 the last one, the operator for one zero byte, at the 0 position */
178 gf2_matrix_square(crc_comb[k + 1], crc_comb[k]);
179 gf2_matrix_square(crc_comb[k + 2], crc_comb[k + 1]);
180 gf2_matrix_square(crc_comb[0], crc_comb[k + 2]);
182 /* generate operators for applying 2^n zero bytes to a CRC, filling out
183 the remainder of the table -- the operators repeat after GF2_DIM
184 values of n, so the table only needs GF2_DIM entries, regardless of
185 the size of the length being processed */
186 for (n = 1; n < k; n++)
187 gf2_matrix_square(crc_comb[n], crc_comb[n - 1]);
189 /* mark tables as complete, in case someone else is waiting */
192 else { /* not first */
193 /* wait for the other guy to finish (not efficient, but rare) */
194 while (crc_table_empty)
201 out = fopen("crc32.h", "w");
202 if (out == NULL) return;
204 /* write out CRC table to crc32.h */
205 fprintf(out, "/* crc32.h -- tables for rapid CRC calculation\n");
206 fprintf(out, " * Generated automatically by crc32.c\n */\n\n");
207 fprintf(out, "local const z_crc_t FAR ");
208 fprintf(out, "crc_table[%d][256] =\n{\n {\n", TBLS);
209 write_table(out, crc_table[0], 256);
211 fprintf(out, "#ifdef BYFOUR\n");
212 for (k = 1; k < 8; k++) {
213 fprintf(out, " },\n {\n");
214 write_table(out, crc_table[k], 256);
216 fprintf(out, "#endif\n");
218 fprintf(out, " }\n};\n");
220 /* write out zero operator table to crc32.h */
221 fprintf(out, "\nlocal const z_crc_t FAR ");
222 fprintf(out, "crc_comb[%d][%d] =\n{\n {\n", GF2_DIM, GF2_DIM);
223 write_table(out, crc_comb[0], GF2_DIM);
224 for (k = 1; k < GF2_DIM; k++) {
225 fprintf(out, " },\n {\n");
226 write_table(out, crc_comb[k], GF2_DIM);
228 fprintf(out, " }\n};\n");
231 #endif /* MAKECRCH */
235 local void write_table(out, table, k)
237 const z_crc_t FAR *table;
242 for (n = 0; n < k; n++)
243 fprintf(out, "%s0x%08lxUL%s", n % 5 ? "" : " ",
244 (unsigned long)(table[n]),
245 n == k - 1 ? "\n" : (n % 5 == 4 ? ",\n" : ", "));
253 #endif /* MAKECRCH */
255 #else /* !DYNAMIC_CRC_TABLE */
256 /* ========================================================================
257 * Tables of CRC-32s of all single-byte values, made by make_crc_table(),
258 * and tables of zero operator matrices for crc32_combine().
261 #endif /* DYNAMIC_CRC_TABLE */
263 /* =========================================================================
264 * This function can be used by asm versions of crc32()
266 const z_crc_t FAR * ZEXPORT get_crc_table()
268 #ifdef DYNAMIC_CRC_TABLE
271 #endif /* DYNAMIC_CRC_TABLE */
272 return (const z_crc_t FAR *)crc_table;
275 /* ========================================================================= */
276 #define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
277 #define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
279 /* ========================================================================= */
280 unsigned long ZEXPORT crc32_z(crc, buf, len)
282 const unsigned char FAR *buf;
285 if (buf == Z_NULL) return 0UL;
287 #ifdef DYNAMIC_CRC_TABLE
290 #endif /* DYNAMIC_CRC_TABLE */
293 if (sizeof(void *) == sizeof(z_size_t)) {
297 if (*((unsigned char *)(&endian)))
298 return crc32_little(crc, buf, len);
300 return crc32_big(crc, buf, len);
303 crc = crc ^ 0xffffffffUL;
311 return crc ^ 0xffffffffUL;
314 /* ========================================================================= */
315 unsigned long ZEXPORT crc32(crc, buf, len)
317 const unsigned char FAR *buf;
320 return crc32_z(crc, buf, len);
326 This BYFOUR code accesses the passed unsigned char * buffer with a 32-bit
327 integer pointer type. This violates the strict aliasing rule, where a
328 compiler can assume, for optimization purposes, that two pointers to
329 fundamentally different types won't ever point to the same memory. This can
330 manifest as a problem only if one of the pointers is written to. This code
331 only reads from those pointers. So long as this code remains isolated in
332 this compilation unit, there won't be a problem. For this reason, this code
333 should not be copied and pasted into a compilation unit in which other code
334 writes to the buffer that is passed to these routines.
337 /* ========================================================================= */
338 #define DOLIT4 c ^= *buf4++; \
339 c = crc_table[3][c & 0xff] ^ crc_table[2][(c >> 8) & 0xff] ^ \
340 crc_table[1][(c >> 16) & 0xff] ^ crc_table[0][c >> 24]
341 #define DOLIT32 DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4; DOLIT4
343 /* ========================================================================= */
344 local unsigned long crc32_little(crc, buf, len)
346 const unsigned char FAR *buf;
350 register const z_crc_t FAR *buf4;
354 while (len && ((z_size_t)buf & 3)) {
355 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
359 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
368 buf = (const unsigned char FAR *)buf4;
371 c = crc_table[0][(c ^ *buf++) & 0xff] ^ (c >> 8);
374 return (unsigned long)c;
377 /* ========================================================================= */
378 #define DOBIG4 c ^= *buf4++; \
379 c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
380 crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
381 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
383 /* ========================================================================= */
384 local unsigned long crc32_big(crc, buf, len)
386 const unsigned char FAR *buf;
390 register const z_crc_t FAR *buf4;
392 c = ZSWAP32((z_crc_t)crc);
394 while (len && ((z_size_t)buf & 3)) {
395 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
399 buf4 = (const z_crc_t FAR *)(const void FAR *)buf;
408 buf = (const unsigned char FAR *)buf4;
411 c = crc_table[4][(c >> 24) ^ *buf++] ^ (c << 8);
414 return (unsigned long)(ZSWAP32(c));
419 /* ========================================================================= */
420 local uLong crc32_combine_(crc1, crc2, len2)
427 #ifdef DYNAMIC_CRC_TABLE
430 #endif /* DYNAMIC_CRC_TABLE */
433 /* operator for 2^n zeros repeats every GF2_DIM n values */
434 for (n = 0; len2; n = (n + 1) % GF2_DIM, len2 >>= 1)
436 crc1 = gf2_matrix_times(crc_comb[n], crc1);
440 /* ========================================================================= */
441 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
446 return crc32_combine_(crc1, crc2, len2);
449 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
454 return crc32_combine_(crc1, crc2, len2);
457 /* ========================================================================= */
458 local void crc32_combine_gen_(op, len2)
466 #ifdef DYNAMIC_CRC_TABLE
469 #endif /* DYNAMIC_CRC_TABLE */
471 /* if len2 is zero or negative, return the identity matrix */
474 for (j = 0; j < GF2_DIM; j++) {
481 /* at least one bit in len2 is set -- find it, and copy the operator
482 corresponding to that position into op */
486 for (j = 0; j < GF2_DIM; j++)
487 op[j] = crc_comb[i][j];
491 i = (i + 1) % GF2_DIM;
494 /* for each remaining bit set in len2 (if any), multiply op by the operator
495 corresponding to that position */
498 i = (i + 1) % GF2_DIM;
502 for (j = 0; j < GF2_DIM; j++)
503 op[j] = gf2_matrix_times(crc_comb[i], op[j]);
507 /* ========================================================================= */
508 void ZEXPORT crc32_combine_gen(op, len2)
512 crc32_combine_gen_(op, len2);
515 void ZEXPORT crc32_combine_gen64(op, len2)
519 crc32_combine_gen_(op, len2);
522 /* ========================================================================= */
523 uLong crc32_combine_op(crc1, crc2, op)
528 return gf2_matrix_times(op, crc1) ^ crc2;