Initial import

third_party/zlib/crc32concat.c

@@ -0,0 +1,83 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=4 sts=4 sw=4 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 1995-2017 Jean-loup Gailly and Mark Adler                          │
+│ Copyright 2017 The Chromium Authors                                          │
+│ Use of this source code is governed by the BSD-style licenses that can       │
+│ be found in the third_party/zlib/LICENSE file.                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "third_party/zlib/deflate.h"
+#include "third_party/zlib/internal.h"
+#include "third_party/zlib/zutil.h"
+
+asm(".ident\t\"\\n\\n\
+zlib (zlib License)\\n\
+Copyright 1995-2017 Jean-loup Gailly and Mark Adler\"");
+asm(".include \"libc/disclaimer.inc\"");
+
+#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
+
+static unsigned long gf2_matrix_times(unsigned long *mat, unsigned long vec) {
+  unsigned long sum;
+  sum = 0;
+  while (vec) {
+    if (vec & 1) sum ^= *mat;
+    vec >>= 1;
+    mat++;
+  }
+  return sum;
+}
+
+static void gf2_matrix_square(unsigned long *square, unsigned long *mat) {
+  int n;
+  for (n = 0; n < GF2_DIM; n++) {
+    square[n] = gf2_matrix_times(mat, mat[n]);
+  }
+}
+
+uLong crc32_combine(uLong crc1, uLong crc2, int64_t len2) {
+  int n;
+  unsigned long row;
+  unsigned long even[GF2_DIM]; /* even-power-of-two zeros operator */
+  unsigned long odd[GF2_DIM];  /* odd-power-of-two zeros operator */
+
+  /* degenerate case (also disallow negative lengths) */
+  if (len2 <= 0) return crc1;
+
+  /* put operator for one zero bit in odd */
+  odd[0] = 0xedb88320UL; /* CRC-32 polynomial */
+  row = 1;
+  for (n = 1; n < GF2_DIM; n++) {
+    odd[n] = row;
+    row <<= 1;
+  }
+
+  /* put operator for two zero bits in even */
+  gf2_matrix_square(even, odd);
+
+  /* put operator for four zero bits in odd */
+  gf2_matrix_square(odd, even);
+
+  /* apply len2 zeros to crc1 (first square will put the operator for one
+     zero byte, eight zero bits, in even) */
+  do {
+    /* apply zeros operator for this bit of len2 */
+    gf2_matrix_square(even, odd);
+    if (len2 & 1) crc1 = gf2_matrix_times(even, crc1);
+    len2 >>= 1;
+
+    /* if no more bits set, then done */
+    if (len2 == 0) break;
+
+    /* another iteration of the loop with odd and even swapped */
+    gf2_matrix_square(odd, even);
+    if (len2 & 1) crc1 = gf2_matrix_times(odd, crc1);
+    len2 >>= 1;
+
+    /* if no more bits set, then done */
+  } while (len2 != 0);
+
+  /* return combined crc */
+  crc1 ^= crc2;
+  return crc1;
+}