mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-12-23 10:05:46 -05:00
398 lines
9.1 KiB
C++
398 lines
9.1 KiB
C++
// Copyright 2020 Mobilinkd LLC.
|
|
|
|
#pragma once
|
|
|
|
#include <algorithm>
|
|
#include <cstdlib>
|
|
#include <cstdint>
|
|
#include <cassert>
|
|
#include <array>
|
|
#include <bitset>
|
|
#include <tuple>
|
|
#include <limits>
|
|
|
|
|
|
namespace modemm17
|
|
{
|
|
|
|
// The make_bitset stuff only works as expected in GCC10 and later.
|
|
|
|
namespace detail {
|
|
|
|
/**
|
|
* This is the max value for the LLR based on size N.
|
|
*/
|
|
template <size_t N>
|
|
constexpr size_t llr_limit()
|
|
{
|
|
return (1 << (N - 1)) - 1;
|
|
}
|
|
|
|
/**
|
|
* There are (2^(N-1)-1) elements (E) per segment (e.g. N=4, E=7; N=3, E=3).
|
|
* These contain the LLR values 1..E. There are 6 segments in the LLR map:
|
|
* 1. (-Inf,-2]
|
|
* 2. (-2, -1]
|
|
* 3. (-1, 0]
|
|
* 4. (0, 1]
|
|
* 5. (1, 2]
|
|
* 6. (2, Inf)
|
|
*
|
|
* Note the slight asymmetry. This is OK as we are dealing with floats and
|
|
* it only matters to an epsilon of the float type.
|
|
*/
|
|
template <size_t N>
|
|
constexpr size_t llr_size()
|
|
{
|
|
return llr_limit<N>() * 6 + 1;
|
|
}
|
|
|
|
template<size_t LLR>
|
|
constexpr std::array<std::tuple<float, std::tuple<int8_t, int8_t>>, llr_size<LLR>()> make_llr_map()
|
|
{
|
|
constexpr size_t size = llr_size<LLR>();
|
|
std::array<std::tuple<float, std::tuple<int8_t, int8_t>>, size> result;
|
|
|
|
constexpr int8_t limit = llr_limit<LLR>();
|
|
constexpr float inc = 1.0 / float(limit);
|
|
int8_t i = limit;
|
|
int8_t j = limit;
|
|
|
|
// Output must be ordered by k, ascending.
|
|
float k = -3.0 + inc;
|
|
for (size_t index = 0; index != size; ++index)
|
|
{
|
|
auto& a = result[index];
|
|
std::get<0>(a) = k;
|
|
std::get<0>(std::get<1>(a)) = i;
|
|
std::get<1>(std::get<1>(a)) = j;
|
|
|
|
if (k + 1.0 < 0)
|
|
{
|
|
j--;
|
|
if (j == 0) j = -1;
|
|
if (j < -limit) j = -limit;
|
|
}
|
|
else if (k - 1.0 < 0)
|
|
{
|
|
i--;
|
|
if (i == 0) i = -1;
|
|
if (i < -limit) i = -limit;
|
|
}
|
|
else
|
|
{
|
|
j++;
|
|
if (j == 0) j = 1;
|
|
if (j > limit) j = limit;
|
|
}
|
|
k += inc;
|
|
}
|
|
return result;
|
|
}
|
|
|
|
}
|
|
|
|
// template<class...Bools>
|
|
// constexpr auto make_bitset(Bools&&...bools)
|
|
// {
|
|
// return detail::make_bitset(std::make_index_sequence<sizeof...(Bools)>(),
|
|
// std::make_tuple(bool(bools)...));
|
|
// }
|
|
|
|
inline int from_4fsk(int symbol)
|
|
{
|
|
// Convert a 4-FSK symbol to a pair of bits.
|
|
switch (symbol)
|
|
{
|
|
case 1: return 0;
|
|
case 3: return 1;
|
|
case -1: return 2;
|
|
case -3: return 3;
|
|
default: abort();
|
|
}
|
|
}
|
|
|
|
template <size_t LLR>
|
|
auto llr(float sample)
|
|
{
|
|
static auto symbol_map = detail::make_llr_map<LLR>();
|
|
static constexpr float MAX_VALUE = 3.0;
|
|
static constexpr float MIN_VALUE = -3.0;
|
|
|
|
float s = std::min(MAX_VALUE, std::max(MIN_VALUE, sample));
|
|
|
|
auto it = std::lower_bound(symbol_map.begin(), symbol_map.end(), s,
|
|
[](std::tuple<float, std::tuple<int8_t, int8_t>> const& e, float s){
|
|
return std::get<0>(e) < s;
|
|
});
|
|
|
|
if (it == symbol_map.end()) return std::get<1>(*symbol_map.rbegin());
|
|
|
|
return std::get<1>(*it);
|
|
}
|
|
|
|
template <size_t IN1, size_t OUT1, size_t P>
|
|
size_t depuncture( // FIXED: MSVC (MULTIPLE DEFINITIONS SAME TEMPLATE)
|
|
const std::array<int8_t, IN1>& in,
|
|
std::array<int8_t, OUT1>& out,
|
|
const std::array<int8_t, P>& p
|
|
)
|
|
{
|
|
size_t index = 0;
|
|
size_t pindex = 0;
|
|
size_t bit_count = 0;
|
|
for (size_t i = 0; i != OUT1 && index < IN1; ++i)
|
|
{
|
|
if (!p[pindex++])
|
|
{
|
|
out[i] = 0;
|
|
bit_count++;
|
|
}
|
|
else
|
|
{
|
|
out[i] = in[index++];
|
|
}
|
|
if (pindex == P) {
|
|
pindex = 0;
|
|
}
|
|
}
|
|
return bit_count;
|
|
}
|
|
|
|
|
|
template <size_t IN0, size_t OUT0, size_t P>
|
|
size_t puncture( // FIXED::MSVC (MULTIPLE DEFINITIONS OF THE SAME TEMPLATE)
|
|
const std::array<uint8_t, IN0>& in,
|
|
std::array<int8_t, OUT0>& out,
|
|
const std::array<int8_t, P>& p
|
|
)
|
|
{
|
|
size_t index = 0;
|
|
size_t pindex = 0;
|
|
size_t bit_count = 0;
|
|
for (size_t i = 0; i != IN0 && index != OUT0; ++i)
|
|
{
|
|
if (p[pindex++])
|
|
{
|
|
out[index++] = in[i];
|
|
bit_count++;
|
|
}
|
|
|
|
if (pindex == P) pindex = 0;
|
|
}
|
|
return bit_count;
|
|
}
|
|
|
|
template <size_t N>
|
|
constexpr bool get_bit_index(
|
|
const std::array<uint8_t, N>& input,
|
|
size_t index
|
|
)
|
|
{
|
|
auto byte_index = index >> 3;
|
|
assert(byte_index < N);
|
|
auto bit_index = 7 - (index & 7);
|
|
|
|
return (input[byte_index] & (1 << bit_index)) >> bit_index;
|
|
}
|
|
|
|
template <size_t N>
|
|
void set_bit_index(
|
|
std::array<uint8_t, N>& input,
|
|
size_t index
|
|
)
|
|
{
|
|
auto byte_index = index >> 3;
|
|
assert(byte_index < N);
|
|
auto bit_index = 7 - (index & 7);
|
|
input[byte_index] |= (1 << bit_index);
|
|
}
|
|
|
|
template <size_t N>
|
|
void reset_bit_index(
|
|
std::array<uint8_t, N>& input,
|
|
size_t index
|
|
)
|
|
{
|
|
auto byte_index = index >> 3;
|
|
assert(byte_index < N);
|
|
auto bit_index = 7 - (index & 7);
|
|
input[byte_index] &= ~(1 << bit_index);
|
|
}
|
|
|
|
template <size_t N>
|
|
void assign_bit_index(
|
|
std::array<uint8_t, N>& input,
|
|
size_t index,
|
|
bool value
|
|
)
|
|
{
|
|
if (value) set_bit_index(input, index);
|
|
else reset_bit_index(input, index);
|
|
}
|
|
|
|
/**
|
|
* Sign-extend an n-bit value to a specific signed integer type.
|
|
*/
|
|
template <typename T, size_t n>
|
|
constexpr T to_int(uint8_t v)
|
|
{
|
|
constexpr auto MAX_LOCAL_INPUT = (1 << (n - 1));
|
|
constexpr auto NEGATIVE_OFFSET = std::numeric_limits<typename std::make_unsigned<T>::type>::max() - (MAX_LOCAL_INPUT - 1);
|
|
T r = v & (1 << (n - 1)) ? NEGATIVE_OFFSET : 0;
|
|
return r + (v & (MAX_LOCAL_INPUT - 1));
|
|
}
|
|
|
|
template <typename T, size_t N>
|
|
constexpr auto to_byte_array(std::array<T, N> in)
|
|
{
|
|
std::array<uint8_t, (N + 7) / 8> out{};
|
|
out.fill(0);
|
|
size_t i = 0;
|
|
size_t b = 0;
|
|
for (auto c : in)
|
|
{
|
|
out[i] |= (c << (7 - b));
|
|
if (++b == 8)
|
|
{
|
|
++i;
|
|
b = 0;
|
|
}
|
|
}
|
|
return out;
|
|
}
|
|
|
|
template <typename T, size_t N>
|
|
constexpr void to_byte_array(
|
|
std::array<T, N> in,
|
|
std::array<uint8_t, (N + 7) / 8>& out
|
|
)
|
|
{
|
|
size_t i = 0;
|
|
size_t b = 0;
|
|
uint8_t tmp = 0;
|
|
for (auto c : in)
|
|
{
|
|
tmp |= (c << (7 - b));
|
|
if (++b == 8)
|
|
{
|
|
out[i] = tmp;
|
|
tmp = 0;
|
|
++i;
|
|
b = 0;
|
|
}
|
|
}
|
|
if (i < out.size()) out[i] = tmp;
|
|
}
|
|
|
|
struct PRBS9
|
|
{
|
|
static constexpr uint16_t MASK = 0x1FF;
|
|
static constexpr uint8_t TAP_1 = 8; // Bit 9
|
|
static constexpr uint8_t TAP_2 = 4; // Bit 5
|
|
static constexpr uint8_t LOCK_COUNT = 18; // 18 consecutive good bits.
|
|
static constexpr uint8_t UNLOCK_COUNT = 25; // bad bits in history required to unlock.
|
|
|
|
uint16_t state = 1;
|
|
bool synced = false;
|
|
uint8_t sync_count = 0;
|
|
uint32_t bit_count = 0;
|
|
uint32_t err_count = 0;
|
|
std::array<uint8_t, 16> history;
|
|
size_t hist_count = 0;
|
|
size_t hist_pos = 0;
|
|
|
|
void count_errors(bool error)
|
|
{
|
|
bit_count += 1;
|
|
hist_count -= (history[hist_pos >> 3] & (1 << (hist_pos & 7))) != 0;
|
|
if (error) {
|
|
err_count += 1;
|
|
hist_count += 1;
|
|
history[hist_pos >> 3] |= (1 << (hist_pos & 7));
|
|
if (hist_count >= UNLOCK_COUNT) synced = false;
|
|
} else {
|
|
history[hist_pos >> 3] &= ~(1 << (hist_pos & 7));
|
|
}
|
|
if (++hist_pos == 128) hist_pos = 0;
|
|
}
|
|
|
|
// PRBS generator.
|
|
bool generate()
|
|
{
|
|
bool result = ((state >> TAP_1) ^ (state >> TAP_2)) & 1;
|
|
state = ((state << 1) | result) & MASK;
|
|
return result;
|
|
}
|
|
|
|
// PRBS Syncronizer. Returns 0 if the bit matches the PRBS, otherwise 1.
|
|
// When synchronizing the LFSR used in the PRBS, a single bad input bit will
|
|
// result in 3 error bits being emitted.
|
|
bool synchronize(bool bit)
|
|
{
|
|
bool result = (bit ^ (state >> TAP_1) ^ (state >> TAP_2)) & 1;
|
|
state = ((state << 1) | bit) & MASK;
|
|
if (result) {
|
|
sync_count = 0; // error
|
|
} else {
|
|
if (++sync_count == LOCK_COUNT) {
|
|
synced = true;
|
|
bit_count += LOCK_COUNT;
|
|
history.fill(0);
|
|
hist_count = 0;
|
|
hist_pos = 0;
|
|
sync_count = 0;
|
|
}
|
|
}
|
|
return result;
|
|
}
|
|
|
|
// PRBS validator. Returns 0 if the bit matches the PRBS, otherwise 1.
|
|
// The results are only valid when sync() returns true;
|
|
bool validate(bool bit)
|
|
{
|
|
bool result;
|
|
if (!synced) {
|
|
result = synchronize(bit);
|
|
} else {
|
|
// PRBS is now free-running.
|
|
result = bit ^ generate();
|
|
count_errors(result);
|
|
}
|
|
return result;
|
|
}
|
|
|
|
bool sync() const { return synced; }
|
|
uint32_t errors() const { assert(synced); return err_count; }
|
|
uint32_t bits() const { assert(synced); return bit_count; }
|
|
|
|
// Reset the state.
|
|
void reset()
|
|
{
|
|
state = 1;
|
|
synced = false;
|
|
sync_count = 0;
|
|
bit_count = 0;
|
|
err_count = 0;
|
|
history.fill(0);
|
|
hist_count = 0;
|
|
hist_pos = 0;
|
|
}
|
|
};
|
|
|
|
template< class T >
|
|
constexpr int popcount( T x ) noexcept
|
|
{
|
|
int count = 0;
|
|
|
|
while (x)
|
|
{
|
|
count += x & 1;
|
|
x >>= 1;
|
|
}
|
|
|
|
return count;
|
|
}
|
|
|
|
} // modemm17
|