# Re: The GSoC project on LDPC codes

**URL:** <https://www.ruby-forum.com/t/re-the-gsoc-project-on-ldpc-codes/237309>\
**Category:** GNU Radio\
**Created:** [November 5, 2013, 4:48pm UTC](https://www.ruby-forum.com/t/re-the-gsoc-project-on-ldpc-codes/237309 "2013-11-05T16:48:38Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [November 5, 2013, 4:48pm UTC](https://www.ruby-forum.com/t/re-the-gsoc-project-on-ldpc-codes/237309/1 "2013-11-05T16:48:38Z")

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Greetings

I was very interested in this project for possible application to the  
op25 project, since P25 uses several FEC codes  
including RS and other block codes. I’ve brought up the gr-ldpc library  
and have a few questions. Due to the hateful YAhoo mail composer, I’m  
hesitant to post lengthy emails to the general list with no opportunity  
for preview prior to hitting SEND, so I’ll try breaking up the list of  
questions into several posts, one per question…

First question: I was getting lots of errors, seg faults, aborts, and  
other misbehavior from the code, which were traced to an apparent bug in  
alist.cc, all of which cleared up when I applied the following patch:

— …/…/repo/gr-ldpc/lib/alist.cc 2013-10-18 10:25:47.508781061 -0400  
+++ ./alist.cc 2013-11-05 11:21:03.879972116 -0500  
@@ -123,7 +123,7 @@  
}

// Parse indices with non zero entries in ith row

- for (int row = 0; row \< N; row++) {

- for (int row = 0; row \< M; row++) {  
std::getline(file, line);  
ss \<\< line;  
for (int entry = 0; entry \< num\_mlist[row]; entry++) {

Can you confirm, is this really a bug?

Thanks and Best

Max

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**Author:** ![ikjtel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/bc8723/32.png) [@ikjtel](https://www.ruby-forum.com/u/ikjtel)\
**Post date:** [November 5, 2013, 6:16pm UTC](https://www.ruby-forum.com/t/re-the-gsoc-project-on-ldpc-codes/237309/2 "2013-11-05T18:16:54Z")

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Dear Max,

You are correct. It is a bug. Now I’m wondering why I didn’t get any  
segmentation faults.

Probably I didn’t get any segmentation faults because, after i = M - 1,  
EOF  
has reached.

Thanks for the correction.

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<div class="post-metadata">

**Author:** ![ikjtel](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/i/bc8723/32.png) [@ikjtel](https://www.ruby-forum.com/u/ikjtel)\
**Post date:** [November 5, 2013, 6:40pm UTC](https://www.ruby-forum.com/t/re-the-gsoc-project-on-ldpc-codes/237309/3 "2013-11-05T18:40:16Z")

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Dear Manu,

Do you have any performance numbers on your LDPC decoder? I could not  
find any info, even in your presentation. Do you have also a BER  
figure, or even better would be some technical report. I would love to  
get some sense on the performance of your implementation.

Best,  
Miklos