Justin Marshall
59 lines
1.3 KiB
C++
59 lines
1.3 KiB
C++
#include "crc16.h"
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#include <array>
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#include <cassert>
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#include <cstddef>
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namespace {
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using CrcTable = std::array<std::uint16_t, 256>;
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CrcTable BuildCrcTable() {
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CrcTable table = {};
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for (std::size_t index = 0; index < table.size(); ++index) {
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std::uint16_t value = static_cast<std::uint16_t>(index << 8);
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for (int bit = 0; bit < 8; ++bit) {
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value = (value & 0x8000u) != 0
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? static_cast<std::uint16_t>((value << 1) ^ 0x1021u)
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: static_cast<std::uint16_t>(value << 1);
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}
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table[index] = value;
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}
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return table;
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}
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const CrcTable& GetCrcTable() {
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static const CrcTable table = BuildCrcTable();
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return table;
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}
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} // namespace
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void CRC16_UpdateChecksum(
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std::uint16_t& crcValue,
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const void* data,
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const int length
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) {
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assert(length >= 0);
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assert(data != nullptr || length == 0);
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if (length <= 0) {
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return;
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}
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const CrcTable& table = GetCrcTable();
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const auto* bytes = static_cast<const std::uint8_t*>(data);
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for (int index = 0; index < length; ++index) {
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const std::uint8_t tableIndex = static_cast<std::uint8_t>(
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(crcValue >> 8) ^ bytes[index]
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);
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crcValue = static_cast<std::uint16_t>(
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table[tableIndex] ^ static_cast<std::uint16_t>(crcValue << 8)
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);
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}
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}
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