From 91b5f380b6c511624064f1b64ae3ebfd710d7272 Mon Sep 17 00:00:00 2001
From: Tom Rondeau <tom@trondeau.com>
Date: Sat, 17 May 2014 19:23:44 -0400
Subject: fec: wip: adding concept of padding for CC encoder/decoder.
When using terminated mode, the CC encoder adds K-1 bits to the output, which doesn't fit a full byte and will throw off the book-keeping in PDU or tagged mode. Padding to fill a byte tells both encoder and decoder to handle the extra bits.
---
gr-fec/lib/cc_decoder_impl.cc | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
(limited to 'gr-fec/lib/cc_decoder_impl.cc')
diff --git a/gr-fec/lib/cc_decoder_impl.cc b/gr-fec/lib/cc_decoder_impl.cc
index 6b7daaf4b2..6739f7bf3d 100644
--- a/gr-fec/lib/cc_decoder_impl.cc
+++ b/gr-fec/lib/cc_decoder_impl.cc
@@ -40,23 +40,24 @@ namespace gr {
cc_decoder::make(int frame_size, int k,
int rate, std::vector<int> polys,
int start_state, int end_state,
- cc_mode_t mode)
+ cc_mode_t mode, bool padded)
{
return generic_decoder::sptr
(new cc_decoder_impl(frame_size, k, rate, polys,
- start_state, end_state, mode));
+ start_state, end_state, mode, padded));
}
cc_decoder_impl::cc_decoder_impl(int frame_size, int k,
int rate, std::vector<int> polys,
int start_state, int end_state,
- cc_mode_t mode)
+ cc_mode_t mode, bool padded)
: generic_decoder("cc_decoder"),
d_k(k),
d_rate(rate),
d_partial_rate(rate),
d_polys(polys),
d_mode(mode),
+ d_padding(0),
d_start_state_chaining(start_state),
d_start_state_nonchaining(start_state),
d_end_state_nonchaining(end_state)
@@ -65,7 +66,12 @@ namespace gr {
// based on this value.
d_max_frame_size = frame_size;
d_frame_size = frame_size;
- //set_frame_size(frame_size);
+
+ // set up a padding factor. If padding, the encoded frame was exteded
+ // by this many bits to fit into a full byte.
+ if(padded && (mode == CC_TERMINATED)) {
+ d_padding = static_cast<int>(8.0f*ceilf(d_rate*(d_k-1)/8.0f) - (d_rate*(d_k-1)));
+ }
d_vp = new struct v;
@@ -170,7 +176,7 @@ namespace gr {
cc_decoder_impl::get_input_size()
{
if(d_mode == CC_TERMINATED) {
- return d_rate * (d_frame_size + d_k - 1);
+ return d_rate * (d_frame_size + d_k - 1) + d_padding;
}
else {
return d_rate * d_frame_size;
@@ -365,7 +371,6 @@ namespace gr {
d += tailsize * d_decision_t_size ; /* Look past tail */
int retval;
int dif = tailsize - (d_k - 1);
- //printf("break, %d, %d\n", dif, (nbits+dif)%d_frame_size);
decision_t dec;
while(nbits-- > d_frame_size - (d_k - 1)) {
int k;
@@ -373,8 +378,6 @@ namespace gr {
k = (dec.w[(endstate>>d_ADDSHIFT)/32] >> ((endstate>>d_ADDSHIFT)%32)) & 1;
endstate = (endstate >> 1) | (k << (d_k-2+d_ADDSHIFT));
- //data[((nbits+dif)%nbits)>>3] = endstate>>d_SUBSHIFT;
- //printf("%d, %d\n", k, (nbits+dif)%d_frame_size);
data[((nbits+dif)%d_frame_size)] = k;
retval = endstate;
@@ -400,7 +403,7 @@ namespace gr {
{
bool ret = true;
if(frame_size > d_max_frame_size) {
- GR_LOG_INFO(d_logger, boost::format("tried to set frame to %1%; max possible is %2%") \
+ GR_LOG_INFO(d_logger, boost::format("cc_decoder: tried to set frame to %1%; max possible is %2%") \
% frame_size % d_max_frame_size);
frame_size = d_max_frame_size;
ret = false;
@@ -412,7 +415,7 @@ namespace gr {
case(CC_TAILBITING):
d_veclen = d_frame_size + (6 * (d_k - 1));
if(d_veclen * d_rate > d_managed_in_size) {
- throw std::runtime_error("attempt to resize beyond d_managed_in buffer size!\n");
+ throw std::runtime_error("cc_decoder: attempt to resize beyond d_managed_in buffer size!\n");
}
break;
@@ -421,7 +424,13 @@ namespace gr {
break;
case(CC_STREAMING):
+ d_veclen = d_frame_size + d_k - 1;
+ break;
+
case(CC_TERMINATED):
+ // If the input is being padded out to a byte, we know the
+ // real frame size is without the padding.
+ d_frame_size -= d_padding * d_rate;
d_veclen = d_frame_size + d_k - 1;
break;
--
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