% MATLAB SIMULATION OF NSA FS-1016 CELP v3.2
% COPYRIGHT (C) 1995-99 ANDREAS SPANIAS AND TED PAINTER
%
% This Copyright applies only to this particular MATLAB implementation
% of the FS-1016 CELP coder.  The MATLAB software is intended only for educational
% purposes.  No other use is intended or authorized.  This is not a public
% domain program and distribution to individuals or networks is strictly
% prohibited.  Be aware that use of the standard in any form is goverened
% by rules of the US DoD.  Therefore patents and royalties may apply to
% authors, companies, or committees associated with this standard, FS-1016.  For
% questions regarding the MATLAB implementation please contact Andreas
% Spanias at (480) 965-1837.  For questions on rules,
% royalties, or patents associated with the standard, please contact the DoD.
%
% ALL DERIVATIVE WORKS MUST INCLUDE THIS COPYRIGHT NOTICE.
%
% ******************************************************************
% CBSEARCH
%
% PORTED TO MATLAB FROM CELP 3.2a C RELEASE
% 7-11-94
%
% ******************************************************************
%
% DESCRIPTION
%
% Find optimal MSPE excitation code word
%
% DESIGN NOTES
%
% Code book search is performed by closed-loop analysis using conventional
% minimum squared prediction error (MSPE) criteria of the perceptually
% weighted error signal.  The code book is overlaped to allow recursive
% computational savings in routine cgain:
%
% index  code book
%       +-------------------------+
%   1   | 2(M-1)       2(M-1)+L-1 |
%   2   | 2(M-2)       2(M-2)+L-1 |
%   :   | :            :          |
%   N-1 | .            .          |
%   N   | .            .          |
%   :   | 2            61         |
%   :   | 0            59         |
%       +-------------------------+
%
%   where: M = maximum code book size
%          N = actual code book search size (any value between 1 & M)
%          L = code word length
%
%   each code word is:  2(M-index) -> 2(M-index)+L-1
%
% REFERENCES
%
% 1. Tremain, Thomas E., Joseph P. Campbell, Jr and Vanoy C. Welch,
%    "A 4.8 kbps Code Excited Linear Predictive Coder," Proceedings
%    of the Mobile Satellite Conference, 3-5 May 1988, pp. 491-496.
%
% 2. Campbell, Joseph P. Jr., Vanoy C. Welch and Thomas E. Tremain,
%   "An Expandable Error-Protected 4800 bps CELP Coder (U.S. Federal
%    Standard 4800 bps Voice Coder)," Proceedings of ICASSP, 1989.
%    (and Proceedings of Speech Tech, 1989.)
%
% VARIABLES
%
% INPUTS/OUTPUTS
%   l          -     Length of vectors
%   v          -     Optimum excitation segment found
%
% INTERNALS
%   gain       -     Gains for each codeword (vector)
%   err        -     Error terms for each codeword (vector)
%   codeword   -     Current codeword
%   emax       -     Maximum error found during codebook search
%   i          -     General purpose loop counter
%
% GLOBALS
%   StochCB    -     Stochastic codebook
%   cbindex    -     Stochastic codebook index
%   ncsize     -     Stochastic codebook size
%   mxsw       -     Excitation flag
%   gindex     -     Stochastic codebook gain index
%   cbgbits    -     Codebook gain quantization bit allocation
%   cbgtype    -     Codebook gain quantization type
%
% CONSTANTS
%   LEN        -     Length of truncated impulse response
%   MAXNCSIZE  -     Maximum codebook size (max number of codewords)
%   TRUE       -     General purpose boolean flag
%   FALSE      -     General purpose boolean flag
%
% ******************************************************************

function v = cbsearch( l, v )

% DECLARE GLOBAL VARIABLES
global cbindex StochCB ncsize mxsw gindex cbgbits cbgtype

% DECLARE GLOBAL CONSTANTS
global TRUE FALSE MAXNCSIZE

% INITIALIZE LOCAL CONSTANTS
LEN = 30;

% INITIALIZE LOCAL VARIABLES
gain = zeros( MAXNCSIZE, 1 );
err = zeros( MAXNCSIZE, 1 );

% FIND GAIN AND -ERROR TERM FOR EACH CODE WORD AND SEARCH FOR BEST
% CODE WORD (MAX -ERROR TERM). CODEWORDS ARE OVERLAPPED BY SHIFTS
% OF -2 ALONG THE CODE VECTOR X.  GAIN(I) AND ERR(I) CAN BE REPLACED
% BY SCALARS.
codeword = ( 2 * MAXNCSIZE ) - 2;
cbindex = 1;
[ gain(1), err(1) ] = cgain( StochCB(codeword+1:codeword+l), l, TRUE, LEN );
emax = err(1);
codeword = codeword - 2;
for i = 1:ncsize-1
    [ gain(i+1), err(i+1) ] = cgain( StochCB(codeword+1:codeword+l), l, FALSE, LEN );
    codeword = codeword - 2;
    if err(i+1) >= emax
        emax = err(i+1);
	    cbindex = i + 1;
    end
end

% ESTABLISH POINTER TO THE BEST CODEWORD
codeword = 2 * (MAXNCSIZE - cbindex);

% GIVEN BEST CODEWORD, RECOMPUTE ITS GAIN TO CORRECT ANY ACCUMULATED
% ERRORS IN THE RECURSIONS
[ gain(cbindex), err(cbindex) ] = cgain( StochCB(codeword+1:codeword+l), l, TRUE, LEN );

% CONSTRAIN EXCITATION GAIN TO LIMITS IMPOSED BY MEXCITE3
if mxsw == 1
    gain(cbindex) = mexcite3( gain(cbindex) );
end

% DO GAIN QUANTIZATION (UNNESCESSARY FOR CLOSED-LOOP QUANTIZATION)
if strcmp( cbgtype, 'none' ) == 0
    if cbgbits == 5
        [ gindex, gain(cbindex) ] = gaincode( gain(cbindex) );
    else
        fprintf( 'cbsearch: not quantizing cbgain\n' );
    end
end

% SCALE SELECTED CODE WORD VECTOR -> EXCITATION VECTOR
v = ( gain(cbindex) * StochCB(codeword+1:codeword+l) )';