44 lines
1.1 KiB
C++
44 lines
1.1 KiB
C++
// Copyright 2017 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "components/zucchini/crc32.h"
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#include <array>
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#include "base/check_op.h"
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namespace zucchini {
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namespace {
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std::array<uint32_t, 256> MakeCrc32Table() {
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constexpr uint32_t kCrc32Poly = 0xEDB88320;
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std::array<uint32_t, 256> crc32Table;
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for (uint32_t i = 0; i < 256; ++i) {
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uint32_t r = i;
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for (int j = 0; j < 8; ++j)
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r = (r >> 1) ^ (kCrc32Poly & ~((r & 1) - 1));
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crc32Table[i] = r;
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}
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return crc32Table;
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}
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} // namespace
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// Minimalistic CRC-32 implementation for Zucchini usage. Adapted from LZMA SDK
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// (found at third_party/lzma_sdk/7zCrc.c), which is public domain.
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uint32_t CalculateCrc32(const uint8_t* first, const uint8_t* last) {
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DCHECK_GE(last, first);
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static const std::array<uint32_t, 256> kCrc32Table = MakeCrc32Table();
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uint32_t ret = 0xFFFFFFFF;
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for (; first != last; ++first)
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ret = kCrc32Table[(ret ^ *first) & 0xFF] ^ (ret >> 8);
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return ret ^ 0xFFFFFFFF;
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}
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} // namespace zucchini
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