Checksums.h

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#pragma once
 
#include <cstdint>
#include <span>
 
namespace QGC {
 
struct Fletcher8
{
    uint8_t a = 0;
    uint8_t b = 0;
 
    constexpr bool operator==(const Fletcher8&) const = default;
};
 
[[nodiscard]] constexpr Fletcher8 fletcher8(std::span<const uint8_t> bytes, Fletcher8 state = {})
{
    for (const uint8_t byte : bytes) {
        state.a = static_cast<uint8_t>(state.a + byte);
        state.b = static_cast<uint8_t>(state.b + state.a);
    }
    return state;
}
 
[[nodiscard]] constexpr uint16_t crc16Xmodem(std::span<const uint8_t> bytes)
{
    uint16_t crc = 0;
    for (const uint8_t byte : bytes) {
        uint8_t x = static_cast<uint8_t>((crc >> 8) ^ byte);
        x ^= x >> 4;
        crc = static_cast<uint16_t>((crc << 8) ^ (x << 12) ^ (x << 5) ^ x);
    }
    return crc;
}
 
[[nodiscard]] constexpr uint32_t crc24q(std::span<const uint8_t> bytes)
{
    uint32_t crc = 0;
    for (const uint8_t byte : bytes) {
        crc ^= uint32_t(byte) << 16;
        for (int bit = 0; bit < 8; ++bit) {
            crc <<= 1;
            if (crc & 0x1000000) {
                crc ^= 0x1864cfb;
            }
        }
    }
    return crc & 0xffffff;
}
 
[[nodiscard]] constexpr uint8_t nmeaChecksum(std::span<const uint8_t> body)
{
    uint8_t result = 0;
    for (const uint8_t byte : body) {
        result ^= byte;
    }
    return result;
}
 
}  // namespace QGC