sdrangel/modemm17/M17Randomizer.h

80 wiersze
1.7 KiB
C++

// Copyright 2020 Mobilinkd LLC.
#pragma once
#include <array>
#include <cstdint>
#include <cstddef>
namespace modemm17
{
namespace detail
{
// M17 randomization matrix.
static const std::array<uint8_t, 46> DC = std::array<uint8_t, 46>{
0xd6, 0xb5, 0xe2, 0x30, 0x82, 0xFF, 0x84, 0x62,
0xba, 0x4e, 0x96, 0x90, 0xd8, 0x98, 0xdd, 0x5d,
0x0c, 0xc8, 0x52, 0x43, 0x91, 0x1d, 0xf8, 0x6e,
0x68, 0x2F, 0x35, 0xda, 0x14, 0xea, 0xcd, 0x76,
0x19, 0x8d, 0xd5, 0x80, 0xd1, 0x33, 0x87, 0x13,
0x57, 0x18, 0x2d, 0x29, 0x78, 0xc3};
}
template <size_t N = 368>
struct M17Randomizer
{
std::array<int8_t, N> dc_;
M17Randomizer()
{
size_t i = 0;
for (auto b : detail::DC)
{
for (size_t j = 0; j != 8; ++j)
{
dc_[i++] = (b >> (7 - j)) & 1 ? -1 : 1;
}
}
}
// Randomize and derandomize are the same operation.
void operator()(std::array<int8_t, N>& frame)
{
for (size_t i = 0; i != N; ++i)
{
frame[i] *= dc_[i];
}
}
void randomize(std::array<int8_t, N>& frame)
{
for (size_t i = 0; i != N; ++i)
{
frame[i] ^= (dc_[i] == -1);
}
}
};
template <size_t N = 46>
struct M17ByteRandomizer
{
// Randomize and derandomize are the same operation.
void operator()(std::array<uint8_t, N>& frame)
{
for (size_t i = 0; i != N; ++i)
{
for (size_t j = 8; j != 0; --j)
{
uint8_t mask = 1 << (j - 1);
frame[i] = (frame[i] & ~mask) | ((frame[i] & mask) ^ (detail::DC[i] & mask));
}
}
}
};
} // modemm17