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M17 - Include libM17 Viterbi Decoder and Misc Math;

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lwvmobile
2024-03-07 22:22:19 -05:00
parent a30512f4e4
commit 677b064e97
3 changed files with 362 additions and 3 deletions
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232
src/3.c
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@@ -85,3 +85,235 @@ void trellis_decode(uint8_t result[], const uint8_t source[], int result_len)
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
//Ripped from libM17
//prototypes
// uint32_t viterbi_decode(uint8_t* out, const uint16_t* in, const uint16_t len);
// uint32_t viterbi_decode_punctured(uint8_t* out, const uint16_t* in, const uint8_t* punct, const uint16_t in_len, const uint16_t p_len);
// void viterbi_decode_bit(uint16_t s0, uint16_t s1, const size_t pos);
// uint32_t viterbi_chainback(uint8_t* out, size_t pos, uint16_t len);
// void viterbi_reset(void);
// uint16_t q_abs_diff(const uint16_t v1, const uint16_t v2);
#define K 5 //constraint length
#define NUM_STATES (1 << (K - 1)) //number of states
static uint32_t prevMetrics[NUM_STATES];
static uint32_t currMetrics[NUM_STATES];
static uint32_t prevMetricsData[NUM_STATES];
static uint32_t currMetricsData[NUM_STATES];
static uint16_t viterbi_history[244];
/**
* @brief Decode unpunctured convolutionally encoded data.
*
* @param out Destination array where decoded data is written.
* @param in Input data.
* @param len Input length in bits.
* @return Number of bit errors corrected.
*/
uint32_t viterbi_decode(uint8_t* out, const uint16_t* in, const uint16_t len)
{
if(len > 244*2)
fprintf(stderr, "Input size exceeds max history\n");
viterbi_reset();
size_t pos = 0;
for(size_t i = 0; i < len; i += 2)
{
uint16_t s0 = in[i];
uint16_t s1 = in[i + 1];
viterbi_decode_bit(s0, s1, pos);
pos++;
}
return viterbi_chainback(out, pos, len/2);
}
/**
* @brief Decode punctured convolutionally encoded data.
*
* @param out Destination array where decoded data is written.
* @param in Input data.
* @param punct Puncturing matrix.
* @param in_len Input data length.
* @param p_len Puncturing matrix length (entries).
* @return Number of bit errors corrected.
*/
uint32_t viterbi_decode_punctured(uint8_t* out, const uint16_t* in, const uint8_t* punct, const uint16_t in_len, const uint16_t p_len)
{
if(in_len > 244*2)
fprintf(stderr, "Input size exceeds max history\n");
uint16_t umsg[244*2]; //unpunctured message
uint8_t p=0; //puncturer matrix entry
uint16_t u=0; //bits count - unpunctured message
uint16_t i=0; //bits read from the input message
while(i<in_len)
{
if(punct[p])
{
umsg[u]=in[i];
i++;
}
else
{
umsg[u]=0x7FFF;
}
u++;
p++;
p%=p_len;
}
return viterbi_decode(out, umsg, u) - (u-in_len)*0x7FFF;
}
/**
* @brief Decode one bit and update trellis.
*
* @param s0 Cost of the first symbol.
* @param s1 Cost of the second symbol.
* @param pos Bit position in history.
*/
void viterbi_decode_bit(uint16_t s0, uint16_t s1, const size_t pos)
{
static const uint16_t COST_TABLE_0[] = {0, 0, 0, 0, 0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF};
static const uint16_t COST_TABLE_1[] = {0, 0xFFFF, 0xFFFF, 0, 0, 0xFFFF, 0xFFFF, 0};
for(uint8_t i = 0; i < NUM_STATES/2; i++)
{
uint32_t metric = q_abs_diff(COST_TABLE_0[i], s0)
+ q_abs_diff(COST_TABLE_1[i], s1);
uint32_t m0 = prevMetrics[i] + metric;
uint32_t m1 = prevMetrics[i + NUM_STATES/2] + (0x1FFFE - metric);
uint32_t m2 = prevMetrics[i] + (0x1FFFE - metric);
uint32_t m3 = prevMetrics[i + NUM_STATES/2] + metric;
uint8_t i0 = 2 * i;
uint8_t i1 = i0 + 1;
if(m0 >= m1)
{
viterbi_history[pos]|=(1<<i0);
currMetrics[i0] = m1;
}
else
{
viterbi_history[pos]&=~(1<<i0);
currMetrics[i0] = m0;
}
if(m2 >= m3)
{
viterbi_history[pos]|=(1<<i1);
currMetrics[i1] = m3;
}
else
{
viterbi_history[pos]&=~(1<<i1);
currMetrics[i1] = m2;
}
}
//swap
uint32_t tmp[NUM_STATES];
for(uint8_t i=0; i<NUM_STATES; i++)
{
tmp[i]=currMetrics[i];
}
for(uint8_t i=0; i<NUM_STATES; i++)
{
currMetrics[i]=prevMetrics[i];
prevMetrics[i]=tmp[i];
}
}
/**
* @brief History chainback to obtain final byte array.
*
* @param out Destination byte array for decoded data.
* @param pos Starting position for the chainback.
* @param len Length of the output in bits.
* @return Minimum Viterbi cost at the end of the decode sequence.
*/
uint32_t viterbi_chainback(uint8_t* out, size_t pos, uint16_t len)
{
uint8_t state = 0;
size_t bitPos = len+4;
memset(out, 0, (len-1)/8+1);
while(pos > 0)
{
bitPos--;
pos--;
uint16_t bit = viterbi_history[pos]&((1<<(state>>4)));
state >>= 1;
if(bit)
{
state |= 0x80;
out[bitPos/8]|=1<<(7-(bitPos%8));
}
}
uint32_t cost = prevMetrics[0];
for(size_t i = 0; i < NUM_STATES; i++)
{
uint32_t m = prevMetrics[i];
if(m < cost) cost = m;
}
return cost;
}
/**
* @brief Reset the decoder state. No args.
*
*/
void viterbi_reset(void)
{
memset((uint8_t*)viterbi_history, 0, 2*244);
memset((uint8_t*)currMetrics, 0, 4*NUM_STATES);
memset((uint8_t*)prevMetrics, 0, 4*NUM_STATES);
memset((uint8_t*)currMetricsData, 0, 4*NUM_STATES);
memset((uint8_t*)prevMetricsData, 0, 4*NUM_STATES);
}
uint16_t q_abs_diff(const uint16_t v1, const uint16_t v2)
{
if(v2 > v1) return v2 - v1;
return v1 - v2;
}
//original sources
//--------------------------------------------------------------------
// M17 C library - decode/viterbi.c
//
// This file contains:
// - the Viterbi decoder
//
// Wojciech Kaczmarski, SP5WWP
// M17 Project, 29 December 2023
//--------------------------------------------------------------------
//--------------------------------------------------------------------
// M17 C library - math/math.c
//
// This file contains:
// - absolute difference value
// - Euclidean norm (L2) calculation for n-dimensional vectors (float)
// - soft-valued arrays to integer conversion (and vice-versa)
// - fixed-valued multiplication and division
//
// Wojciech Kaczmarski, SP5WWP
// M17 Project, 29 December 2023
//--------------------------------------------------------------------