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instead of rotating back, store current shift value

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and compute the delta shift needed to achieve the same result.

Idea taken from:

Conflict Resolution by Matrix Reordering for DVB-T2 LDPC Decoders
By Cédric Marchand, Jean-Baptiste Doré, Laura Conde-Canencia, Emmanuel Boutillon - 2009
This commit is contained in:
Ahmet Inan 2019-09-24 19:58:46 +02:00
commit 87153003e9
1 changed files with 16 additions and 2 deletions
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18
ldpc_decoder.hh
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@ -51,6 +51,7 @@ class LDPCDecoder
TYPE pty[PTY]; TYPE pty[PTY];
Loc loc[LOC]; Loc loc[LOC];
wdm_t wdm[PTY]; wdm_t wdm[PTY];
int16_t csh[MSG];
uint8_t cnc[q]; uint8_t cnc[q];
static TYPE eor(TYPE a, TYPE b) static TYPE eor(TYPE a, TYPE b)
@ -86,7 +87,11 @@ class LDPCDecoder
for (int k = 0; k < deg; ++k) { for (int k = 0; k < deg; ++k) {
TYPE tmp; TYPE tmp;
if (k < cnt) { if (k < cnt) {
tmp = rotate(msg[lo[k].off], -lo[k].shi); int offset = lo[k].off;
int shift = -lo[k].shi;
shift -= csh[offset];
shift %= D;
tmp = rotate(msg[offset], shift);
} else if (k == cnt) { } else if (k == cnt) {
tmp = pty[W*i+j]; tmp = pty[W*i+j];
} else { } else {
@ -131,6 +136,8 @@ class LDPCDecoder
if (k < cnt) { if (k < cnt) {
int offset = lo[k].off; int offset = lo[k].off;
int shift = -lo[k].shi; int shift = -lo[k].shi;
shift -= csh[offset];
shift %= D;
tmp = rotate(msg[offset], shift); tmp = rotate(msg[offset], shift);
if (last_offset == offset) if (last_offset == offset)
write_conflict = true; write_conflict = true;
@ -180,7 +187,10 @@ class LDPCDecoder
if (k < cnt) { if (k < cnt) {
if (!write_conflict || !((*wd>>k)&1)) { if (!write_conflict || !((*wd>>k)&1)) {
bl[k] = out; bl[k] = out;
msg[lo[k].off] = rotate(tmp, lo[k].shi); int offset = lo[k].off;
int shift = -lo[k].shi;
msg[offset] = tmp;
csh[offset] = shift;
} }
} else if (k == cnt) { } else if (k == cnt) {
bl[k] = out; bl[k] = out;
@ -275,6 +285,8 @@ public:
{ {
for (int i = 0; i < BNL; ++i) for (int i = 0; i < BNL; ++i)
bnl[i] = vzero<TYPE>(); bnl[i] = vzero<TYPE>();
for (int i = 0; i < MSG; ++i)
csh[i] = 0;
for (int i = 0; i < K/M; ++i) for (int i = 0; i < K/M; ++i)
for (int j = 0; j < W; ++j) for (int j = 0; j < W; ++j)
for (int n = 0; n < D; ++n) for (int n = 0; n < D; ++n)
@ -285,6 +297,8 @@ public:
pty[W*i+j].v[n] = parity[q*(W*n+j)+i]; pty[W*i+j].v[n] = parity[q*(W*n+j)+i];
while (bad() && --trials >= 0) while (bad() && --trials >= 0)
update(); update();
for (int i = 0; i < MSG; ++i)
msg[i] = rotate(msg[i], -csh[i]);
for (int i = 0; i < K/M; ++i) for (int i = 0; i < K/M; ++i)
for (int j = 0; j < W; ++j) for (int j = 0; j < W; ++j)
for (int n = 0; n < D; ++n) for (int n = 0; n < D; ++n)