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golombdeco.m

## Copyright (C) 2006 Muthiah Annamalai <muthiah.annamalai@uta.edu>
## 
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; If not, see <http://www.gnu.org/licenses/>.
##

## -*- texinfo -*-
## @deftypefn {Function File} {} golombdeco (@var{code}, @var{m})
##
## Returns the Golomb decoded signal vector using @var{code} and @var{m}. 
## Compulsory m is need to be specified. A restrictions is that a
## signal set must strictly be non-negative. The value of code
## is a cell array of row-vectors which have the  encoded golomb value
## for a single sample. The Golomb algorithm is,
##  used to encode the 'code' and only that can be meaningfully 
## decoded. @var{code} is assumed to have been of format generated
## by the function @code{golombenco}. Also the parameter @var{m} need to
## be a non-zero number, unless which it makes divide-by-zero errors.
## This function works backward the Golomb algorithm see
## @code{golombenco} for more detials on that.
## Reference: Solomon Golomb, Run length Encodings, 1966 IEEE Trans Info' Theory
##
## An exmaple of the use of @code{golombdeco} is
## @example
## @group
##   golombdeco(golombenco(1:4,2),2)
## @end group
## @end example
## @end deftypefn
## @seealso{golombenco}

##! /usr/bin/octave -q
#A stress test routine
#for i=1:100
#  sig=abs(randint(1,10,[0,255]));
#  k=mod(i,10)+1;
#  code=golombenco(sig,k);
#  assert(golombdeco(code,k),sig)
#end
#
#for k=1:10;
# assert(golombdeco(golombenco(4:10,k),k),[4:10]);
#end
#
function sig_op=golombdeco(code,m)
  if ( nargin < 2 ) || (strcmp(class(code),"cell")~=1 || m<=0)
    error('usage: golombdeco(code,m)');
  end
  
  L=length(code);  
  C=ceil(log2(m));
  partition_limit=2**C-m;
 

  power_seq=[2.^(ceil(log2(m))-1:-1:0)];
  power_seq_mod=power_seq(2:end);
  
  for j=1:L
    word=code{j};
    WL=length(word);
    idx=find(word==0)(1);
    q=sum(word(1:idx));
    
    idx2=(WL-idx);
    word_tail=word(idx+1:end);
  
    if(length(word_tail) == C)
      r=sum(word_tail.*power_seq);
      r=r-(partition_limit);
    else
      r=sum(word_tail.*power_seq_mod);
    end
    
    quot(j)=q;
    rem(j)=r;
  end
  sig_op=quot.*m + rem;

  return
end
%! 
%! assert(golombdeco(golombenco(1:4,2),2),[1:4])
%! 

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