--- /dev/null
+## 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 3 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} {} shannonfanodeco (@var{hcode},@var{dict})
+##
+## Returns the original signal that was Shannonfano encoded. The signal
+## was encoded using @code{shannonfanoenco}. This function uses
+## a dict built from the @code{shannonfanodict} and uses it to decode a signal
+## list into a shannonfano list. Restrictions include hcode is expected to be a binary code;
+## returned signal set that strictly belongs in the @code{range [1,N]},
+## with @code{N=length(dict)}. Also dict can only be from the
+## @code{shannonfanodict(...)} routine. Whenever decoding fails,
+## those signal values are indicated by -1, and we successively
+## try to restart decoding from the next bit that hasnt failed in
+## decoding, ad-infinitum.
+##
+## An example use of @code{shannonfanodeco} is
+## @example
+## @group
+## hd=shannonfanodict(1:4,[0.5 0.25 0.15 0.10])
+## hcode=shannonfanoenco(1:4,hd) # [ 1 0 1 0 0 0 0 0 1 ]
+## shannonfanodeco(hcode,hd) # [1 2 3 4]
+##
+## @end group
+## @end example
+## @end deftypefn
+## @seealso{shannonfanoenco, shannonfanodict}
+
+function sig=shannonfanodeco(hcode,dict)
+ if ( nargin < 2 || strcmp(class(dict),"cell")~=1 )
+ error('usage: shannonfanoenco(sig,dict)');
+ end
+ if (max(hcode) > 1 || min(hcode) < 0)
+ error("hcode has elements that are outside alphabet set ...
+ Cannot decode.");
+ end
+
+# TODO:
+# O(log(N)) algorithms exist, but we need some effort to implement those
+# Maybe sometime later, it would be a nice 1-day project
+# Ref: A memory efficient Shannonfano Decoding Algorithm, AINA 2005, IEEE
+#
+
+# TODO: Somebody can implement a 'faster' algorithm than O(N^3) at present
+# Decoding Algorithm O(N+k*log(N)) which is approximately O(N+Nlog(N))
+#
+# 1. Separate the dictionary by the lengths
+# and knows symbol correspondence.
+#
+# 2. Find the symbol in the dict of lengths l,h where
+# l = smallest cw length ignoring 0 length CW, and
+# h = largest cw length , with k=h-l+1;
+#
+# 3. Match the k codewords to the dict using binary
+# search, and then you can declare decision.
+#
+# 4. In case of non-decodable words skip the start-bit
+# used in the previous case, and then restart the same
+# procedure from the next bit.
+#
+ L=length(dict);
+ lenL=length(dict{1});
+ lenH=0;
+
+#
+# Know the ranges of operation
+#
+ for itr=1:L
+ t=length(dict{itr});
+ if(t < lenL)
+ lenL=t;
+ end
+ if(t > lenH)
+ lenH=t;
+ end
+ end
+
+#
+# Now do a O(N^4) algorithm
+#
+ itr=0; #offset into the hcode
+ sig=[]; #output
+ CL=length(hcode);
+
+ %whole decoding loop.
+ while ( itr < CL )
+ %decode one element (or just try to).
+ for itr_y=lenL:lenH
+ %look for word in dictionary.
+ %with flag to indicate found
+ %or not found. Detect end of buffer.
+
+ if ( (itr+itr_y) > CL )
+ break;
+ end
+
+ word=hcode(itr+1:itr+itr_y);
+ flag=0;
+
+ %word
+
+ %search loop.
+ for itr_z=1:L
+ if(isequal(dict{itr_z},word))
+ itr=itr+itr_y;
+ sig=[sig itr_z];
+ flag=1;
+ break;
+ end
+ end %for_ loop breaker
+
+ if( flag == 1 )
+ break; %also need to break_ above then.
+ end
+
+ end %for_ loop
+
+
+ #could not decode
+ if( flag == 0 )
+ itr=itr+1;
+ sig=[sig -1];
+ end
+
+ end %while_ loop
+end
+%!
+%! assert(shannonfanodeco(shannonfanoenco(1:4, shannonfanodict(1:4,[0.5 0.25 0.15 0.10])), shannonfanodict(1:4,[0.5 0.25 0.15 0.10])), [1:4],0)
+%!