/*
* 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);
}
/*
* Populate recursive trellis state
*/
static void gen_rec_state_info(lte_conv_code code, sbyte *val, int reg, short *o)
{
int i;
int prev, rec, mask;
/* Previous '0' and '1' states */
prev = vstate_lshift(reg, code.k, 0);
/* Compute recursive input value (not the value shifted into register) */
rec = (reg >> (code.k - 2)) & 0x01;
if ((int)__builtin_parity(prev & code.rgen) == rec)
{
*val = 0;
}
else
{
*val = 1;
}
/* Compute outputs and unpack to NRZ */
prev = prev | rec << (code.k - 1);
if (code.k == 5)
{
mask = 0x0f;
}
else
{
mask = 0x3f;
}
/* Check for recursive outputs */
for (i = 0; i < code.n; i++)
{
if ((code.gen[i] & mask) != 0)
{
o[i] = (short)(__builtin_parity(prev & code.gen[i]) * 2 - 1);
}
else
{
o[i] = (short)(*val * 2 - 1);
}
}
}
public ConvDec(int len)
{
//Make settings
code = new lte_conv_code
{
n = 3,
k = 7,
len = len,
gen = new int[] { 91, 121, 117, 0 },
term = CONV_TERM.TAIL_BITING,
};
//Create
vdec = alloc_vdec(code);
}
static void reset_vdec(vdecoder dec, lte_conv_code code)
{
dec.n = code.n;
dec.k = code.k;
dec.recursive = code.rgen != 0 ? 1 : 0;
dec.intrvl = short.MaxValue / (dec.n * sbyte.MaxValue) - dec.k;
if (dec.n != 3 || dec.k != 7)
{
throw new Exception();
}
if (code.term == CONV_TERM.FLUSH)
{
dec.len = code.len + code.k - 1;
}
else
{
dec.len = code.len + TAIL_BITING_EXTRA * 2;
}
}
/*
* Allocate decoder object
*
* Subtract the constraint length K on the normalization interval to
* accommodate the initialization path metric at state zero.
*/
static vdecoder alloc_vdec(lte_conv_code code)
{
int i, ns;
ns = NUM_STATES(code.k);
vdecoder dec = new vdecoder();
dec.n = code.n;
dec.k = code.k;
dec.recursive = code.rgen != 0 ? 1 : 0;
dec.intrvl = short.MaxValue / (dec.n * sbyte.MaxValue) - dec.k;
if (dec.n != 3 || dec.k != 7)
{
throw new Exception();
}
if (code.term == CONV_TERM.FLUSH)
{
dec.len = code.len + code.k - 1;
}
else
{
dec.len = code.len + TAIL_BITING_EXTRA * 2;
}
dec.trellis = generate_trellis(code);
dec.pathsBuffer = UnsafeBuffer.Create(sizeof(short *) * dec.len * ns);
dec.pathsPtr = (short *)dec.pathsBuffer;
dec.paths = new short *[dec.len];
for (i = 0; i < dec.len; i++)
{
dec.paths[i] = &dec.pathsPtr[i * ns];
}
return(dec);
}
/*
* Populate non-recursive trellis state
*
* For a given state defined by the k-1 length shift register, find the
* value of the input bit that drove the trellis to that state. Then
* generate the N outputs of the generator polynomial at that state.
*/
static void gen_state_info(lte_conv_code code,
sbyte *val, int reg, short *o)
{
int i;
int prev;
/* Previous '0' state */
prev = vstate_lshift(reg, code.k, 0);
/* Compute output and unpack to NRZ */
*val = (sbyte)((reg >> (code.k - 2)) & 0x01);
prev = prev | (int)*val << (code.k - 1);
for (i = 0; i < code.n; i++)
{
o[i] = (short)(__builtin_parity(prev & code.gen[i]) * 2 - 1);
}
/*Console.WriteLine($"{__builtin_parity(0)}, {__builtin_parity(1)}, {__builtin_parity(2)}");
* for (i = 0; i < code.n; i++)
* Console.WriteLine(o[i]);
* Console.ReadLine();*/
}
