private int viterbi_set_traceback(viterbi v, int traceback)
{
if (traceback < 0 || traceback > PATHMEM - 1)
return -1;
v.traceback = traceback;
return 0;
}
private int viterbi_set_chunksize(viterbi v, int chunksize)
{
if (chunksize < 1 || chunksize > v.traceback)
return -1;
v.chunksize = chunksize;
return 0;
}
private viterbi viterbi_init(int k, int poly1, int poly2)
{
viterbi v;
int i;
v = new viterbi();
v.traceback = PATHMEM - 1;
v.chunksize = 8;
v.nstates = 1 << (k - 1);
v.output = new int[1 << k];
v.metrics = new int[PATHMEM, v.nstates];
v.history = new int[PATHMEM, v.nstates];
v.sequence = new int[PATHMEM];
v.mettab = new int[2, 256];
for (i = 0; i < (1 << k); i++)
v.output[i] = parity(poly1 & i) | (parity(poly2 & i) << 1);
for (i = 0; i < 256; i++)
{
v.mettab[0, i] = 128 - i;
v.mettab[1, i] = i - 128;
}
v.ptr = 0;
return v;
}
private void viterbi_reset(viterbi v)
{
v.metrics = new int[PATHMEM, v.nstates];
v.history = new int[PATHMEM, v.nstates];
v.ptr = 0;
}
private int traceback(viterbi v, int[] metric)
{
int i, bestmetric, beststate;
uint p, c;
p = (uint)((v.ptr - 1) % PATHMEM);
/*
* Find the state with the best metric
*/
bestmetric = Int32.MinValue; // INT_MIN;
beststate = 0;
for (i = 0; i < v.nstates; i++)
{
if (v.metrics[p, i] > bestmetric)
{
bestmetric = v.metrics[p, i];
beststate = i;
}
}
/*
* Trace back 'traceback' steps, starting from the best state
*/
v.sequence[p] = beststate;
for (i = 0; i < v.traceback; i++)
{
uint prev = (uint)((p - 1) % PATHMEM);
v.sequence[prev] = v.history[p, v.sequence[p]];
p = prev;
}
if (metric != null)
metric[0] = v.metrics[p, v.sequence[p]];
/*
* Decode 'chunksize' bits
*/
c = 0;
i = 0;
for (i = 0; i < v.chunksize; i++)
{
/*
* low bit of state is the previous input bit
*/
c = (uint)(c << 1);
c |= (uint)(v.sequence[p] & 1);
p = (uint)((p + 1) % PATHMEM);
}
if (metric != null)
metric[0] = v.metrics[p, v.sequence[p]] - metric[0];
return (int)c;
}
