Re: [OctDev] More limitations in coding functions

[David B. <Dav...@mo...>]

Quentin,

Try the version I just committed. I removed the restriction on
calculating the minimum distance and vastly accelerated this code, and
I reduced the restriction on the syndrome table. There is still a
restriction at the moment in that the syndrome table must not have
more than 2^32 rows. This is enormous, and so I don't think I'll both
removing this restriction, and more memory than any machine I have access
to.

The code I used to test with was

1;
fprintf("  Hamming Coding:                           ");
nsym = 100;
m = 8;
[par, gen, n, k] = hammgen (m);
if (any(any(gen2par(par) != gen)))
  error("FAILED");
endif
if (gfweight(gen) != 3)
  error("FAILED");
endif
msg = randint(nsym,k);
code = encode(msg,n,k,"hamming");
noisy = mod(code + randerr(nsym,n), 2);
dec = decode(noisy,n,k,"hamming");
if (any(any(dec != msg)))
  error("FAILED");
endif         
try			# Protect! If bitshift isn't install!!
  msg = randint(nsym,1,n);
  code = encode(msg,n,k,"hamming/decimal");
  noisy = mod(code + bitshift(1,randint(nsym,1,n)), n+1);
  dec = decode(noisy,n,k,"hamming/decimal");
  if (any(dec != msg))
    error("FAILED");
  endif
catch
end
fprintf("PASSED\n");

The gfweight call still takes a while with m=8, so you might prefer to disable
it. I believe this removes all of the restrictions on the comms toolbox.

Cheers
David

According to Quentin Spencer <qsp...@ie...> (on 07/08/04):
> This time I tried:
> decode(x,255,247,'hamming')
> and received the following error message:
> error: syndtable: message and codeword length must be less than 32
> error: evaluating assignment expression near line 248, column 5
> error: evaluating if command near line 245, column 7
> error: evaluating if command near line 203, column 5
> error: evaluating if command near line 188, column 3
> error: called from `decode' in file 
> `/usr/share/octave/2.1.57/site/m/octave-forge/comm/decode.m'
> 
> So, it appears some modification of the syndtable function is necessary 
> to make this work for hamming codes larger than the (31,36) code.
> 
> -Quentin
> 
> 
> 
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-- 
David Bateman                                Dav...@mo...
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