## 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} {} riceenco (@var{sig}, @var{K})
##
## Returns the Rice encoded signal using @var{K} or optimal K .
## Default optimal K is chosen between 0-7. Currently no other way
## to increase the range except to specify explicitly. Also returns
## @var{K} parameter used (in case it were to be chosen optimally)
## and @var{Ltot} the total length of output code in bits.
## This function uses a @var{K} if supplied or by default chooses
## the optimal K for encoding signal vector into a rice coded vector.
## A restrictions is that a signal set must strictly be non-negative.
## The Rice algorithm is used to encode the data into unary coded
## quotient part which is represented as a set of 1's separated from
## the K-part (binary) using a zero. This scheme doesn't need any
## kind of dictionaries and its close to O(N), but this implementation
## *may be* sluggish, though correct.
##
## Reference: Solomon Golomb, Run length Encodings, 1966 IEEE Trans
## Info' Theory
##
## An example of the use of @code{riceenco} is
## @example
## @group
## riceenco (1:4)
##     @result{} @{[0 1], [1 0 0], [1 0 1], [1 1 0 0]@}
## riceenco (1:10, 2)
##     @result{} @{[0 0 1], [0 1 0], [0 1 1], [1 0 0 0],
##         [1 0 0 1], [1 0 1 0], [1 0 1 1], [1 1 0 0 0],
##         [1 1 0 0 1], [1 1 0 1 0]@}
## @end group
## @end example
## @seealso{ricedeco}
## @end deftypefn

function [rcode, K, Ltot] = riceenco (sig, K)

  if (nargin < 1 || nargin > 2)
    print_usage ();
  elseif (nargin < 2)
    use_optimal_k = 1;
  else
    use_optimal_k = 0;
  endif

  if (min (sig) < 0)
    error ("riceenco: all elements of SIG must be non-negative numbers");
  endif


  L = length (sig);

  ## compute the optimal rice parameter.
  if (use_optimal_k)
    k_opt = 0;
    len_past = sum (sig) + L + k_opt*L;
    quot = sig;

    for k = 1:7
      k_pow_2 = 2**k;
      quot_k = floor (sig./k_pow_2);
      len = sum (quot_k)+L+k*L;
      if (len < len_past)
        len_past = len;
        k_opt = k;
        rem = mod (sig, k_pow_2);
        quot = quot_k;
      endif
    endfor
    Ltot = len_past;
    K = k_opt;
    K_pow_2 = 2**K;
  else
    K_pow_2 = 2**K;
    quot = floor (sig./K_pow_2);
    rem = mod (sig, K_pow_2);
  endif

  for j = 1:L
    rice_part = zeros (1, K);
    ##
    ## How can we eliminate this loop?
    ## I essentially need to get the binary
    ## representation of rem(j) in the rice_part(i)
    ##
    for i = K:-1:1
      rice_part(i) = mod (rem(j), 2);
      rem(j) = floor (rem(j)/2);
    endfor
    rcode{j} = [ones(1, quot(j)) 0 rice_part];
  endfor
  Ltot = sum (quot) + L + K*L;

endfunction

%!assert (riceenco (1:4, 2), {[0 0 1], [0 1 0], [0 1 1], [1 0 0 0]})

%% Test input validation
%!error riceenco ()
%!error riceenco (1, 2, 3)
%!error riceenco (-1)
