61 lines
1.3 KiB
C++
61 lines
1.3 KiB
C++
/*
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This file is part of Telegram Desktop,
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the official desktop application for the Telegram messaging service.
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For license and copyright information please follow this link:
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https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
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*/
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#include "base/crc32hash.h"
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namespace base {
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namespace {
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class Crc32Table {
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public:
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Crc32Table() {
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auto poly = std::uint32_t(0x04c11db7);
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for (auto i = 0; i != 256; ++i) {
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_data[i] = reflect(i, 8) << 24;
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for (auto j = 0; j != 8; ++j) {
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_data[i] = (_data[i] << 1) ^ (_data[i] & (1 << 31) ? poly : 0);
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}
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_data[i] = reflect(_data[i], 32);
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}
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}
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std::uint32_t operator[](int index) const {
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return _data[index];
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}
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private:
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std::uint32_t reflect(std::uint32_t val, char ch) {
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auto result = std::uint32_t(0);
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for (int i = 1; i < (ch + 1); ++i) {
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if (val & 1) {
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result |= 1 << (ch - i);
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}
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val >>= 1;
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}
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return result;
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}
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std::uint32_t _data[256];
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};
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} // namespace
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std::int32_t crc32(const void *data, int len) {
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static const auto kTable = Crc32Table();
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const auto buffer = static_cast<const std::uint8_t*>(data);
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auto crc = std::uint32_t(0xffffffff);
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for (auto i = 0; i != len; ++i) {
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crc = (crc >> 8) ^ kTable[(crc & 0xFF) ^ buffer[i]];
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}
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return static_cast<std::int32_t>(crc ^ 0xffffffff);
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}
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} // namespace base
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