Justin Marshall
43 lines
1.2 KiB
C++
43 lines
1.2 KiB
C++
#include "crc32.h"
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#include <array>
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#include <cstdint>
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namespace {
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const std::uint32_t* CRC32Table() {
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static const std::array<std::uint32_t, 256> table = [] {
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std::array<std::uint32_t, 256> values = {};
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for (std::uint32_t index = 0; index < 256; ++index) {
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std::uint32_t value = index;
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for (int bit = 0; bit < 8; ++bit)
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value = (value >> 1) ^ ((value & 1) != 0 ? 0xEDB88320u : 0u);
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values[index] = value;
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}
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return values;
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}();
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return table.data();
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}
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} // namespace
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void CRC32_UpdateChecksum(unsigned int& checksum, const void* data,
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const int length) {
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if (data == nullptr || length <= 0) return;
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const std::uint32_t* const table = CRC32Table();
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const unsigned char* bytes = static_cast<const unsigned char*>(data);
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for (int index = 0; index < length; ++index)
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checksum = table[(checksum ^ bytes[index]) & 0xFFu] ^ (checksum >> 8);
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}
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void CRC32_FinishChecksum(unsigned int& checksum) {
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checksum = ~checksum;
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}
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unsigned int CRC32_BlockChecksum(const void* data, const int length) {
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unsigned int checksum = 0xFFFFFFFFu;
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CRC32_UpdateChecksum(checksum, data, length);
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CRC32_FinishChecksum(checksum);
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return checksum;
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}
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