84 lines
2.9 KiB
C
84 lines
2.9 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=4 sts=4 sw=4 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 1995-2017 Jean-loup Gailly and Mark Adler │
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│ Copyright 2017 The Chromium Authors │
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│ Use of this source code is governed by the BSD-style licenses that can │
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│ be found in the third_party/zlib/LICENSE file. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "third_party/zlib/deflate.h"
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#include "third_party/zlib/internal.h"
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#include "third_party/zlib/zutil.h"
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asm(".ident\t\"\\n\\n\
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zlib (zlib License)\\n\
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Copyright 1995-2017 Jean-loup Gailly and Mark Adler\"");
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asm(".include \"libc/disclaimer.inc\"");
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#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
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static unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec) {
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unsigned long sum;
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sum = 0;
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while (vec) {
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if (vec & 1) sum ^= *mat;
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vec >>= 1;
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mat++;
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}
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return sum;
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}
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static void gf2_matrix_square(unsigned long *square, unsigned long *mat) {
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int n;
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for (n = 0; n < GF2_DIM; n++) {
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square[n] = gf2_matrix_times(mat, mat[n]);
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}
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}
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uLong crc32_combine(uLong crc1, uLong crc2, int64_t len2) {
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int n;
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unsigned long row;
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unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
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unsigned long odd[GF2_DIM]; /* odd-power-of-two zeros operator */
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/* degenerate case (also disallow negative lengths) */
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if (len2 <= 0) return crc1;
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/* put operator for one zero bit in odd */
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odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
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row = 1;
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for (n = 1; n < GF2_DIM; n++) {
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odd[n] = row;
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row <<= 1;
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}
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/* put operator for two zero bits in even */
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gf2_matrix_square(even, odd);
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/* put operator for four zero bits in odd */
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gf2_matrix_square(odd, even);
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/* apply len2 zeros to crc1 (first square will put the operator for one
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zero byte, eight zero bits, in even) */
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do {
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/* apply zeros operator for this bit of len2 */
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gf2_matrix_square(even, odd);
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if (len2 & 1) crc1 = gf2_matrix_times(even, crc1);
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len2 >>= 1;
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/* if no more bits set, then done */
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if (len2 == 0) break;
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/* another iteration of the loop with odd and even swapped */
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gf2_matrix_square(odd, even);
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if (len2 & 1) crc1 = gf2_matrix_times(odd, crc1);
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len2 >>= 1;
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/* if no more bits set, then done */
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} while (len2 != 0);
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/* return combined crc */
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crc1 ^= crc2;
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return crc1;
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}
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