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sdrangel/modemm17/CRC16.h

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// Copyright 2020 Mobilinkd LLC.
#pragma once
#include <cstdint>
#include <array>
#include <cstddef>
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namespace modemm17
{
struct CRC16
{
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static const uint16_t MASK = 0xFFFF;
static const uint16_t LSB = 0x0001;
static const uint16_t MSB = 0x8000;
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CRC16(uint16_t poly = 0x5935, uint16_t init = 0xFFFF) :
poly_(poly),
init_(init)
{
reg_ = init_;
}
void reset()
{
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reg_ = init_;
for (size_t i = 0; i != 16; ++i)
{
auto bit = reg_ & LSB;
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if (bit) reg_ ^= poly_;
reg_ >>= 1;
if (bit) reg_ |= MSB;
}
reg_ &= MASK;
}
void operator()(uint8_t byte)
{
reg_ = crc(byte, reg_);
}
uint16_t crc(uint8_t byte, uint16_t reg)
{
for (size_t i = 0; i != 8; ++i)
{
auto msb = reg & MSB;
reg = ((reg << 1) & MASK) | ((byte >> (7 - i)) & LSB);
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if (msb) reg ^= poly_;
}
return reg & MASK;
}
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uint16_t get()
{
auto reg = reg_;
for (size_t i = 0; i != 16; ++i)
{
auto msb = reg & MSB;
reg = ((reg << 1) & MASK);
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if (msb) reg ^= poly_;
}
return reg;
}
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std::array<uint8_t, 2> get_bytes()
{
auto crc = get();
std::array<uint8_t, 2> result{uint8_t((crc >> 8) & 0xFF), uint8_t(crc & 0xFF)};
return result;
}
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private:
uint16_t poly_;
uint16_t init_;
uint16_t reg_;
};
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} // modemm17