On Mon, Jul 14, 2014 at 3:19 AM, Jan Krämer <kraemer...@googlemail.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Hey Vesa, > > the cc_decoder_impl.cc and it's corresponding volk kernel > "volk_8u_x4_conv_k7_r2_8u.h" in gr-fec avoid this problem already by > normalizing the path metric after each step in the trellis. I'm not > sure if they are on the master branch yet, but you can check out > Tom Rondeau's gnuradio repo (www.github.com/trondeau). > > - -Jan Yes, this was merged into the master branch: http://gnuradio.org/doc/doxygen/page_fec.html Tom > On 14.07.2014 08:54, Vaskelainen Vesa wrote: > > Hi all, > > > > I noticed that in viterbi.c when input symbol pair quality is good, > > branch metrics 'mets[ ]' maximum value is 512. In case of errorless > > input symbols, this causes cumulative metric increase by 512 for > > the best path for each decoded bit. In BUTTERFLY macro, m0 and m1 > > are type of int, i.e. they can hold integers less than 2^31, but > > since metric increases by 8x2^9=2^12 for each output byte, this > > implies that after 2^31 / 2^12 = 2^19:th byte occurs an integer > > overflow and decoder output gets messy. > > > > This is simple to check, if you connect constant source of -1's to > > ccsds27decoder and write output to a file and then run hexdump of > > the file. > > > > I corrected this by changing the type of m0, m1 and metric to long > > long, when the integer overflow should not exist before 2^51:th > > byte. However, with periodic initialization of metric the integer > > overflow of cumulative metric would be fully avoided. > > > > Best regards, Vesa Vaskelainen > > > > _______________________________________________ Discuss-gnuradio > > mailing list Discuss-gnuradio@gnu.org > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1 > Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ > > iQEcBAEBAgAGBQJTw4SLAAoJEJmPbVa7qwgjz+MH/2qUOYHwxCpAqwUtpXe0eOEX > +wf4FvJhFTMUdNf/WmlUMt28jtYc3a0xjkJVD+vQO1vNP2e4GlQsB2Rywe5ZUf71 > 0fDghklVRjN+idwRZWV51FDxpvdU8Tk1kC4PYI/8s1FZ+M7uGc/bLB8LMO7MCNwG > QgjPW7Hl+efUXoYtDshueWY8RbmccUg7EzWNqAgryumkKai3tsg3yODNNMtBrouE > R9DPO4ZbUwcqogk5EpIQxoYusRT2OmLDxD0XE80IuJ/VHLd0j6qdbXULHrj33XGz > o6XP2+nS1Yj1Mw8zcnxdBcG1M4V3B7r2q9UXtmVh6RU1qZDNoNQo69c+h1n2k8E= > =+K4q > -----END PGP SIGNATURE----- > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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