1 /* crc32.c -- compute the CRC-32 of a data stream
2 * Copyright (C) 1995-2022 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
5 * This interleaved implementation of a CRC makes use of pipelined multiple
6 * arithmetic-logic units, commonly found in modern CPU cores. It is due to
7 * Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution.
13 Note on the use of DYNAMIC_CRC_TABLE: there is no mutex or semaphore
14 protection on the static variables used to control the first-use generation
15 of the crc tables. Therefore, if you #define DYNAMIC_CRC_TABLE, you should
16 first call get_crc_table() to initialize the tables before allowing more than
17 one thread to use crc32().
19 MAKECRCH can be #defined to write out crc32.h. A main() routine is also
20 produced, so that this one source file can be compiled to an executable.
25 # ifndef DYNAMIC_CRC_TABLE
26 # define DYNAMIC_CRC_TABLE
27 # endif /* !DYNAMIC_CRC_TABLE */
30 #include "zutil.h" /* for Z_U4, Z_U8, z_crc_t, and FAR definitions */
33 A CRC of a message is computed on N braids of words in the message, where
34 each word consists of W bytes (4 or 8). If N is 3, for example, then three
35 running sparse CRCs are calculated respectively on each braid, at these
36 indices in the array of words: 0, 3, 6, ..., 1, 4, 7, ..., and 2, 5, 8, ...
37 This is done starting at a word boundary, and continues until as many blocks
38 of N * W bytes as are available have been processed. The results are combined
39 into a single CRC at the end. For this code, N must be in the range 1..6 and
40 W must be 4 or 8. The upper limit on N can be increased if desired by adding
41 more #if blocks, extending the patterns apparent in the code. In addition,
42 crc32.h would need to be regenerated, if the maximum N value is increased.
44 N and W are chosen empirically by benchmarking the execution time on a given
45 processor. The choices for N and W below were based on testing on Intel Kaby
46 Lake i7, AMD Ryzen 7, ARM Cortex-A57, Sparc64-VII, PowerPC POWER9, and MIPS64
47 Octeon II processors. The Intel, AMD, and ARM processors were all fastest
48 with N=5, W=8. The Sparc, PowerPC, and MIPS64 were all fastest at N=5, W=4.
49 They were all tested with either gcc or clang, all using the -O3 optimization
50 level. Your mileage may vary.
60 # error N must be in 1..6
64 z_crc_t must be at least 32 bits. z_word_t must be at least as long as
65 z_crc_t. It is assumed here that z_word_t is either 32 bits or 64 bits, and
66 that bytes are eight bits.
70 Define W and the associated z_word_t type. If W is not defined, then a
71 braided calculation is not used, and the associated tables and code are not
80 # define W 8 /* required for MAKECRCH */
82 # if defined(__x86_64__) || defined(__aarch64__)
90 # if W == 8 && defined(Z_U8)
91 typedef Z_U8 z_word_t;
95 typedef Z_U4 z_word_t;
101 /* If available, use the ARM processor CRC32 instruction. */
102 #if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32) && W == 8
106 /* Local functions. */
107 local z_crc_t multmodp OF((z_crc_t a, z_crc_t b));
108 local z_crc_t x2nmodp OF((z_off64_t n, unsigned k));
110 #if defined(W) && (!defined(ARMCRC32) || defined(DYNAMIC_CRC_TABLE))
111 local z_word_t byte_swap OF((z_word_t word));
114 #if defined(W) && !defined(ARMCRC32)
115 local z_crc_t crc_word OF((z_word_t data));
116 local z_word_t crc_word_big OF((z_word_t data));
119 #if defined(W) && (!defined(ARMCRC32) || defined(DYNAMIC_CRC_TABLE))
121 Swap the bytes in a z_word_t to convert between little and big endian. Any
122 self-respecting compiler will optimize this to a single machine byte-swap
123 instruction, if one is available. This assumes that word_t is either 32 bits
126 local z_word_t byte_swap OF((z_word_t word));
128 local z_word_t byte_swap(word)
133 (word & 0xff00000000000000) >> 56 |
134 (word & 0xff000000000000) >> 40 |
135 (word & 0xff0000000000) >> 24 |
136 (word & 0xff00000000) >> 8 |
137 (word & 0xff000000) << 8 |
138 (word & 0xff0000) << 24 |
139 (word & 0xff00) << 40 |
143 (word & 0xff000000) >> 24 |
144 (word & 0xff0000) >> 8 |
145 (word & 0xff00) << 8 |
151 /* CRC polynomial. */
152 #define POLY 0xedb88320 /* p(x) reflected, with x^32 implied */
154 #ifdef DYNAMIC_CRC_TABLE
156 local z_crc_t FAR crc_table[256];
157 local z_crc_t FAR x2n_table[32];
158 local void make_crc_table OF((void));
160 local z_word_t FAR crc_big_table[256];
161 local z_crc_t FAR crc_braid_table[W][256];
162 local z_word_t FAR crc_braid_big_table[W][256];
163 local void braid OF((z_crc_t [][256], z_word_t [][256], int, int));
166 local void write_table OF((FILE *, const z_crc_t FAR *, int));
167 local void write_table32hi OF((FILE *, const z_word_t FAR *, int));
168 local void write_table64 OF((FILE *, const z_word_t FAR *, int));
169 #endif /* MAKECRCH */
172 Define a once() function depending on the availability of atomics. If this is
173 compiled with DYNAMIC_CRC_TABLE defined, and if CRCs will be computed in
174 multiple threads, and if atomics are not available, then get_crc_table() must
175 be called to initialize the tables and must return before any threads are
176 allowed to compute or combine CRCs.
179 /* Definition of once functionality. */
180 typedef struct once_s once_t;
181 local void once OF((once_t *, void (*)(void)));
183 /* Check for the availability of atomics. */
184 #if defined(__STDC__) && __STDC_VERSION__ >= 201112L && \
185 !defined(__STDC_NO_ATOMICS__)
187 #include <stdatomic.h>
189 /* Structure for once(), which must be initialized with ONCE_INIT. */
194 #define ONCE_INIT {ATOMIC_FLAG_INIT, 0}
197 Run the provided init() function exactly once, even if multiple threads
198 invoke once() at the same time. The state must be a once_t initialized with
201 local void once(state, init)
205 if (!atomic_load(&state->done)) {
206 if (atomic_flag_test_and_set(&state->begun))
207 while (!atomic_load(&state->done))
211 atomic_store(&state->done, 1);
216 #else /* no atomics */
218 /* Structure for once(), which must be initialized with ONCE_INIT. */
223 #define ONCE_INIT {0, 0}
225 /* Test and set. Alas, not atomic, but tries to minimize the period of
227 local int test_and_set OF((int volatile *));
228 local int test_and_set(flag)
238 /* Run the provided init() function once. This is not thread-safe. */
239 local void once(state, init)
244 if (test_and_set(&state->begun))
256 /* State for once(). */
257 local once_t made = ONCE_INIT;
260 Generate tables for a byte-wise 32-bit CRC calculation on the polynomial:
261 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.
263 Polynomials over GF(2) are represented in binary, one bit per coefficient,
264 with the lowest powers in the most significant bit. Then adding polynomials
265 is just exclusive-or, and multiplying a polynomial by x is a right shift by
266 one. If we call the above polynomial p, and represent a byte as the
267 polynomial q, also with the lowest power in the most significant bit (so the
268 byte 0xb1 is the polynomial x^7+x^3+x^2+1), then the CRC is (q*x^32) mod p,
269 where a mod b means the remainder after dividing a by b.
271 This calculation is done using the shift-register method of multiplying and
272 taking the remainder. The register is initialized to zero, and for each
273 incoming bit, x^32 is added mod p to the register if the bit is a one (where
274 x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by x
275 (which is shifting right by one and adding x^32 mod p if the bit shifted out
276 is a one). We start with the highest power (least significant bit) of q and
277 repeat for all eight bits of q.
279 The table is simply the CRC of all possible eight bit values. This is all the
280 information needed to generate CRCs on data a byte at a time for all
281 combinations of CRC register values and incoming bytes.
284 local void make_crc_table()
289 /* initialize the CRC of bytes tables */
290 for (i = 0; i < 256; i++) {
292 for (j = 0; j < 8; j++)
293 p = p & 1 ? (p >> 1) ^ POLY : p >> 1;
296 crc_big_table[i] = byte_swap(p);
300 /* initialize the x^2^n mod p(x) table */
301 p = (z_crc_t)1 << 30; /* x^1 */
303 for (n = 1; n < 32; n++)
304 x2n_table[n] = p = multmodp(p, p);
307 /* initialize the braiding tables -- needs x2n_table[] */
308 braid(crc_braid_table, crc_braid_big_table, N, W);
314 The crc32.h header file contains tables for both 32-bit and 64-bit
315 z_word_t's, and so requires a 64-bit type be available. In that case,
316 z_word_t must be defined to be 64-bits. This code then also generates
317 and writes out the tables for the case that z_word_t is 32 bits.
319 #if !defined(W) || W != 8
320 # error Need a 64-bit integer type in order to generate crc32.h.
325 z_word_t big[8][256];
327 out = fopen("crc32.h", "w");
328 if (out == NULL) return;
330 /* write out little-endian CRC table to crc32.h */
332 "/* crc32.h -- tables for rapid CRC calculation\n"
333 " * Generated automatically by crc32.c\n */\n"
335 "local const z_crc_t FAR crc_table[] = {\n"
337 write_table(out, crc_table, 256);
341 /* write out big-endian CRC table for 64-bit z_word_t to crc32.h */
348 "local const z_word_t FAR crc_big_table[] = {\n"
350 write_table64(out, crc_big_table, 256);
354 /* write out big-endian CRC table for 32-bit z_word_t to crc32.h */
357 "#else /* W == 4 */\n"
359 "local const z_word_t FAR crc_big_table[] = {\n"
361 write_table32hi(out, crc_big_table, 256);
367 /* write out braid tables for each value of N */
368 for (n = 1; n <= 6; n++) {
373 /* compute braid tables for this N and 64-bit word_t */
374 braid(ltl, big, n, 8);
376 /* write out braid tables for 64-bit z_word_t to crc32.h */
381 "local const z_crc_t FAR crc_braid_table[][256] = {\n");
382 for (k = 0; k < 8; k++) {
384 write_table(out, ltl[k], 256);
385 fprintf(out, "}%s", k < 7 ? ",\n" : "");
390 "local const z_word_t FAR crc_braid_big_table[][256] = {\n");
391 for (k = 0; k < 8; k++) {
393 write_table64(out, big[k], 256);
394 fprintf(out, "}%s", k < 7 ? ",\n" : "");
399 /* compute braid tables for this N and 32-bit word_t */
400 braid(ltl, big, n, 4);
402 /* write out braid tables for 32-bit z_word_t to crc32.h */
405 "#else /* W == 4 */\n"
407 "local const z_crc_t FAR crc_braid_table[][256] = {\n");
408 for (k = 0; k < 4; k++) {
410 write_table(out, ltl[k], 256);
411 fprintf(out, "}%s", k < 3 ? ",\n" : "");
416 "local const z_word_t FAR crc_braid_big_table[][256] = {\n");
417 for (k = 0; k < 4; k++) {
419 write_table32hi(out, big[k], 256);
420 fprintf(out, "}%s", k < 3 ? ",\n" : "");
433 /* write out zeros operator table to crc32.h */
436 "local const z_crc_t FAR x2n_table[] = {\n"
438 write_table(out, x2n_table, 32);
443 #endif /* MAKECRCH */
449 Write the 32-bit values in table[0..k-1] to out, five per line in
450 hexadecimal separated by commas.
452 local void write_table(out, table, k)
454 const z_crc_t FAR *table;
459 for (n = 0; n < k; n++)
460 fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : " ",
461 (unsigned long)(table[n]),
462 n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
466 Write the high 32-bits of each value in table[0..k-1] to out, five per line
467 in hexadecimal separated by commas.
469 local void write_table32hi(out, table, k)
471 const z_word_t FAR *table;
476 for (n = 0; n < k; n++)
477 fprintf(out, "%s0x%08lx%s", n == 0 || n % 5 ? "" : " ",
478 (unsigned long)(table[n] >> 32),
479 n == k - 1 ? "" : (n % 5 == 4 ? ",\n" : ", "));
483 Write the 64-bit values in table[0..k-1] to out, three per line in
484 hexadecimal separated by commas. This assumes that if there is a 64-bit
485 type, then there is also a long long integer type, and it is at least 64
486 bits. If not, then the type cast and format string can be adjusted
489 local void write_table64(out, table, k)
491 const z_word_t FAR *table;
496 for (n = 0; n < k; n++)
497 fprintf(out, "%s0x%016llx%s", n == 0 || n % 3 ? "" : " ",
498 (unsigned long long)(table[n]),
499 n == k - 1 ? "" : (n % 3 == 2 ? ",\n" : ", "));
502 /* Actually do the deed. */
509 #endif /* MAKECRCH */
513 Generate the little and big-endian braid tables for the given n and z_word_t
514 size w. Each array must have room for w blocks of 256 elements.
516 local void braid(ltl, big, n, w)
524 for (k = 0; k < w; k++) {
525 p = x2nmodp((n * w + 3 - k) << 3, 0);
527 big[w - 1 - k][0] = 0;
528 for (i = 1; i < 256; i++) {
529 ltl[k][i] = q = multmodp(i << 24, p);
530 big[w - 1 - k][i] = byte_swap(q);
536 #else /* !DYNAMIC_CRC_TABLE */
537 /* ========================================================================
538 * Tables for byte-wise and braided CRC-32 calculations, and a table of powers
539 * of x for combining CRC-32s, all made by make_crc_table().
542 #endif /* DYNAMIC_CRC_TABLE */
544 /* ========================================================================
545 * Routines used for CRC calculation. Some are also required for the table
550 Return a(x) multiplied by b(x) modulo p(x), where p(x) is the CRC polynomial,
551 reflected. For speed, this requires that a not be zero.
553 local z_crc_t multmodp(a, b)
559 m = (z_crc_t)1 << 31;
564 if ((a & (m - 1)) == 0)
568 b = b & 1 ? (b >> 1) ^ POLY : b >> 1;
574 Return x^(n * 2^k) modulo p(x). Requires that x2n_table[] has been
577 local z_crc_t x2nmodp(n, k)
583 p = (z_crc_t)1 << 31; /* x^0 == 1 */
586 p = multmodp(x2n_table[k & 31], p);
593 /* =========================================================================
594 * This function can be used by asm versions of crc32(), and to force the
595 * generation of the CRC tables in a threaded application.
597 const z_crc_t FAR * ZEXPORT get_crc_table()
599 #ifdef DYNAMIC_CRC_TABLE
600 once(&made, make_crc_table);
601 #endif /* DYNAMIC_CRC_TABLE */
602 return (const z_crc_t FAR *)crc_table;
605 /* =========================================================================
606 * Use ARM machine instructions if available. This will compute the CRC about
607 * ten times faster than the braided calculation. This code does not check for
608 * the presence of the CRC instruction at run time. __ARM_FEATURE_CRC32 will
609 * only be defined if the compilation specifies an ARM processor architecture
610 * that has the instructions. For example, compiling with -march=armv8.1-a or
611 * -march=armv8-a+crc, or -march=native if the compile machine has the crc32
617 Constants empirically determined to maximize speed. These values are from
618 measurements on a Cortex-A57. Your mileage may vary.
620 #define Z_BATCH 3990 /* number of words in a batch */
621 #define Z_BATCH_ZEROS 0xa10d3d0c /* computed from Z_BATCH = 3990 */
622 #define Z_BATCH_MIN 800 /* fewest words in a final batch */
624 unsigned long ZEXPORT crc32_z(crc, buf, len)
626 const unsigned char FAR *buf;
631 const z_word_t *word;
632 z_word_t val0, val1, val2;
633 z_size_t last, last2, i;
636 /* Return initial CRC, if requested. */
637 if (buf == Z_NULL) return 0;
639 #ifdef DYNAMIC_CRC_TABLE
640 once(&made, make_crc_table);
641 #endif /* DYNAMIC_CRC_TABLE */
643 /* Pre-condition the CRC */
644 crc = (~crc) & 0xffffffff;
646 /* Compute the CRC up to a word boundary. */
647 while (len && ((z_size_t)buf & 7) != 0) {
650 __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
653 /* Prepare to compute the CRC on full 64-bit words word[0..num-1]. */
654 word = (z_word_t const *)buf;
658 /* Do three interleaved CRCs to realize the throughput of one crc32x
659 instruction per cycle. Each CRC is calculated on Z_BATCH words. The
660 three CRCs are combined into a single CRC after each set of batches. */
661 while (num >= 3 * Z_BATCH) {
664 for (i = 0; i < Z_BATCH; i++) {
666 val1 = word[i + Z_BATCH];
667 val2 = word[i + 2 * Z_BATCH];
668 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
669 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
670 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
674 crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc1;
675 crc = multmodp(Z_BATCH_ZEROS, crc) ^ crc2;
678 /* Do one last smaller batch with the remaining words, if there are enough
679 to pay for the combination of CRCs. */
681 if (last >= Z_BATCH_MIN) {
685 for (i = 0; i < last; i++) {
687 val1 = word[i + last];
688 val2 = word[i + last2];
689 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
690 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc1) : "r"(val1));
691 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc2) : "r"(val2));
695 val = x2nmodp(last, 6);
696 crc = multmodp(val, crc) ^ crc1;
697 crc = multmodp(val, crc) ^ crc2;
700 /* Compute the CRC on any remaining words. */
701 for (i = 0; i < num; i++) {
703 __asm__ volatile("crc32x %w0, %w0, %x1" : "+r"(crc) : "r"(val0));
707 /* Complete the CRC on any remaining bytes. */
708 buf = (const unsigned char FAR *)word;
712 __asm__ volatile("crc32b %w0, %w0, %w1" : "+r"(crc) : "r"(val));
715 /* Return the CRC, post-conditioned. */
716 return crc ^ 0xffffffff;
724 Return the CRC of the W bytes in the word_t data, taking the
725 least-significant byte of the word as the first byte of data, without any pre
726 or post conditioning. This is used to combine the CRCs of each braid.
728 local z_crc_t crc_word OF((z_word_t data));
730 local z_crc_t crc_word(data)
734 for (k = 0; k < W; k++)
735 data = (data >> 8) ^ crc_table[data & 0xff];
736 return (z_crc_t)data;
739 local z_word_t crc_word_big OF((z_word_t data));
741 local z_word_t crc_word_big(data)
745 for (k = 0; k < W; k++)
747 crc_big_table[(data >> ((W - 1) << 3)) & 0xff];
753 /* ========================================================================= */
754 unsigned long ZEXPORT crc32_z(crc, buf, len)
756 const unsigned char FAR *buf;
759 /* Return initial CRC, if requested. */
760 if (buf == Z_NULL) return 0;
762 #ifdef DYNAMIC_CRC_TABLE
763 once(&made, make_crc_table);
764 #endif /* DYNAMIC_CRC_TABLE */
766 /* Pre-condition the CRC */
767 crc = (~crc) & 0xffffffff;
771 /* If provided enough bytes, do a braided CRC calculation. */
772 if (len >= N * W + W - 1) {
774 z_word_t const *words;
778 /* Compute the CRC up to a z_word_t boundary. */
779 while (len && ((z_size_t)buf & (W - 1)) != 0) {
781 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
784 /* Compute the CRC on as many N z_word_t blocks as are available. */
785 blks = len / (N * W);
787 words = (z_word_t const *)buf;
789 /* Do endian check at execution time instead of compile time, since ARM
790 processors can change the endianess at execution time. If the
791 compiler knows what the endianess will be, it can optimize out the
792 check and the unused branch. */
794 if (*(unsigned char *)&endian) {
820 /* Initialize the CRC for each braid. */
839 Process the first blks-1 blocks, computing the CRCs on each braid
843 /* Load the word for each braid into registers. */
844 word0 = crc0 ^ words[0];
846 word1 = crc1 ^ words[1];
848 word2 = crc2 ^ words[2];
850 word3 = crc3 ^ words[3];
852 word4 = crc4 ^ words[4];
854 word5 = crc5 ^ words[5];
862 /* Compute and update the CRC for each word. The loop should
864 crc0 = crc_braid_table[0][word0 & 0xff];
866 crc1 = crc_braid_table[0][word1 & 0xff];
868 crc2 = crc_braid_table[0][word2 & 0xff];
870 crc3 = crc_braid_table[0][word3 & 0xff];
872 crc4 = crc_braid_table[0][word4 & 0xff];
874 crc5 = crc_braid_table[0][word5 & 0xff];
880 for (k = 1; k < W; k++) {
881 crc0 ^= crc_braid_table[k][(word0 >> (k << 3)) & 0xff];
883 crc1 ^= crc_braid_table[k][(word1 >> (k << 3)) & 0xff];
885 crc2 ^= crc_braid_table[k][(word2 >> (k << 3)) & 0xff];
887 crc3 ^= crc_braid_table[k][(word3 >> (k << 3)) & 0xff];
889 crc4 ^= crc_braid_table[k][(word4 >> (k << 3)) & 0xff];
891 crc5 ^= crc_braid_table[k][(word5 >> (k << 3)) & 0xff];
901 Process the last block, combining the CRCs of the N braids at the
904 crc = crc_word(crc0 ^ words[0]);
906 crc = crc_word(crc1 ^ words[1] ^ crc);
908 crc = crc_word(crc2 ^ words[2] ^ crc);
910 crc = crc_word(crc3 ^ words[3] ^ crc);
912 crc = crc_word(crc4 ^ words[4] ^ crc);
914 crc = crc_word(crc5 ^ words[5] ^ crc);
925 z_word_t crc0, word0, comb;
927 z_word_t crc1, word1;
929 z_word_t crc2, word2;
931 z_word_t crc3, word3;
933 z_word_t crc4, word4;
935 z_word_t crc5, word5;
942 /* Initialize the CRC for each braid. */
943 crc0 = byte_swap(crc);
961 Process the first blks-1 blocks, computing the CRCs on each braid
965 /* Load the word for each braid into registers. */
966 word0 = crc0 ^ words[0];
968 word1 = crc1 ^ words[1];
970 word2 = crc2 ^ words[2];
972 word3 = crc3 ^ words[3];
974 word4 = crc4 ^ words[4];
976 word5 = crc5 ^ words[5];
984 /* Compute and update the CRC for each word. The loop should
986 crc0 = crc_braid_big_table[0][word0 & 0xff];
988 crc1 = crc_braid_big_table[0][word1 & 0xff];
990 crc2 = crc_braid_big_table[0][word2 & 0xff];
992 crc3 = crc_braid_big_table[0][word3 & 0xff];
994 crc4 = crc_braid_big_table[0][word4 & 0xff];
996 crc5 = crc_braid_big_table[0][word5 & 0xff];
1002 for (k = 1; k < W; k++) {
1003 crc0 ^= crc_braid_big_table[k][(word0 >> (k << 3)) & 0xff];
1005 crc1 ^= crc_braid_big_table[k][(word1 >> (k << 3)) & 0xff];
1007 crc2 ^= crc_braid_big_table[k][(word2 >> (k << 3)) & 0xff];
1009 crc3 ^= crc_braid_big_table[k][(word3 >> (k << 3)) & 0xff];
1011 crc4 ^= crc_braid_big_table[k][(word4 >> (k << 3)) & 0xff];
1013 crc5 ^= crc_braid_big_table[k][(word5 >> (k << 3)) & 0xff];
1023 Process the last block, combining the CRCs of the N braids at the
1026 comb = crc_word_big(crc0 ^ words[0]);
1028 comb = crc_word_big(crc1 ^ words[1] ^ comb);
1030 comb = crc_word_big(crc2 ^ words[2] ^ comb);
1032 comb = crc_word_big(crc3 ^ words[3] ^ comb);
1034 comb = crc_word_big(crc4 ^ words[4] ^ comb);
1036 comb = crc_word_big(crc5 ^ words[5] ^ comb);
1043 crc = byte_swap(comb);
1047 Update the pointer to the remaining bytes to process.
1049 buf = (unsigned char const *)words;
1054 /* Complete the computation of the CRC on any remaining bytes. */
1057 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1058 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1059 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1060 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1061 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1062 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1063 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1064 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1068 crc = (crc >> 8) ^ crc_table[(crc ^ *buf++) & 0xff];
1071 /* Return the CRC, post-conditioned. */
1072 return crc ^ 0xffffffff;
1077 /* ========================================================================= */
1078 unsigned long ZEXPORT crc32(crc, buf, len)
1080 const unsigned char FAR *buf;
1083 return crc32_z(crc, buf, len);
1086 /* ========================================================================= */
1087 uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
1092 #ifdef DYNAMIC_CRC_TABLE
1093 once(&made, make_crc_table);
1094 #endif /* DYNAMIC_CRC_TABLE */
1095 return multmodp(x2nmodp(len2, 3), crc1) ^ (crc2 & 0xffffffff);
1098 /* ========================================================================= */
1099 uLong ZEXPORT crc32_combine(crc1, crc2, len2)
1104 return crc32_combine64(crc1, crc2, (z_off64_t)len2);
1107 /* ========================================================================= */
1108 uLong ZEXPORT crc32_combine_gen64(len2)
1111 #ifdef DYNAMIC_CRC_TABLE
1112 once(&made, make_crc_table);
1113 #endif /* DYNAMIC_CRC_TABLE */
1114 return x2nmodp(len2, 3);
1117 /* ========================================================================= */
1118 uLong ZEXPORT crc32_combine_gen(len2)
1121 return crc32_combine_gen64((z_off64_t)len2);
1124 /* ========================================================================= */
1125 uLong ZEXPORT crc32_combine_op(crc1, crc2, op)
1130 return multmodp(op, crc1) ^ (crc2 & 0xffffffff);