/*
* Allocate and initialize the trellis object
*
* Initialization consists of generating the outputs and output value of a
* given state. Due to trellis symmetry, only one of the transition paths
* is used by the butterfly operation in the forward recursion, so only one
* set of N outputs is required per state variable.
*/
static vtrellis generate_trellis(lte_conv_code code)
{
vtrellis trellis;
short * o;
int ns = NUM_STATES(code.k);
int olen = (code.n == 2) ? 2 : 4;
trellis = new vtrellis();
trellis.num_states = ns;
trellis.sumsBuffer = UnsafeBuffer.Create(ns, sizeof(short));
trellis.sums = (short *)trellis.sumsBuffer;
trellis.outputsBuffer = UnsafeBuffer.Create(ns * olen, sizeof(short));
trellis.outputs = (short *)trellis.outputsBuffer;
trellis.valsBuffer = UnsafeBuffer.Create(ns, sizeof(sbyte));
trellis.vals = (sbyte *)trellis.valsBuffer;
/* Populate the trellis state objects */
for (int i = 0; i < ns; i++)
{
o = &trellis.outputs[olen * i];
if (code.rgen != 0)
{
gen_rec_state_info(code, &trellis.vals[i], i, o);
}
else
{
gen_state_info(code, &trellis.vals[i], i, o);
}
}
return(trellis);
}
/*
* Forward trellis recursion
*
* Generate branch metrics and path metrics with a combined function. Only
* accumulated path metric sums and path selections are stored. Normalize on
* the interval specified by the decoder.
*/
static void _conv_decode(vdecoder dec, sbyte *seq, CONV_TERM term, int len)
{
int i, j = 0;
vtrellis trellis = dec.trellis;
if (term == CONV_TERM.TAIL_BITING)
{
j = len - TAIL_BITING_EXTRA;
}
for (i = 0; i < dec.len; i++, j++)
{
if (term == CONV_TERM.TAIL_BITING && j == len)
{
j = 0;
}
gen_metrics_k7_n3(&seq[dec.n * j],
trellis.outputs,
trellis.sums,
dec.paths[i],
((i % dec.intrvl) != 0 ? 0 : 1)); //flipped on purpose
}
}
/* Release the trellis */
static void free_trellis(vtrellis trellis)
{
trellis.outputsBuffer.Dispose();
trellis.sumsBuffer.Dispose();
trellis.valsBuffer.Dispose();
}