cbsearch.h

g729 coding ipaddressing

/**************************************************************************
*
* ROUTINE
*				cbsearch
*
* FUNCTION
*				find optimal MSPE excitation code word
*
* SYNOPSIS
*				subroutine cbsearch(l, v)
*
*	formal 
*
*						data	I/O
*		name			type	type	function
*		-------------------------------------------------------------------
*		l				int 	i		length of vectors
*		v(l)			float	o		optimum excitation segment found
*
*	external 
*						data	I/O
*		name			type	type	function
*		-------------------------------------------------------------------
*		cbgbits 		int 	i		code book gain bit allocation
*		cbindex 		int 	i/o 	code book index
*		gindex			int 	i/o 	gain index
*		ncsize			int 	i		code book size
*		no				int 	i		filter order  predictor
*		h[] 			float	i		impulse response
*		x[];			float	i		code book
*		cbgtype[];		char	i		code book gain quantizer type
*		cb_gain_vid 	int 	i
*		cb_qgain_vid	int 	i
*		cb_match_vid	int 	i
*		cb_exc_vid		int 	i
*		cb_ir_vid		int 	i
*		dbcon_vid		int 	i
*		mxsw			int 	i		modified excitation switch
*
***************************************************************************
*		
* DESCRIPTION
*
*  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
*		
***************************************************************************
*
*	global 
*
*
*		CODE BOOK VARIABLES:
*		err 	real	error for each code book entry
*		gain	real	gain for each code book entry
*
***************************************************************************
* CALLED BY
*
*		csub
*
* CALLS
*
*		cgain	[gainencode]   save_sg	 mexcite3
*
***************************************************************************
*
*
* REFERENCES
*
*		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.
*
*		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.)
*
*************************************************************************/

#define LEN 			30 /* length of truncated impulse response */

static void cbsearch(int l, float a_v[])
{
  int i, l_codeword;
  float emax, gain[MAXNCSIZE], err[MAXNCSIZE];
  float oldgain;

  /*			*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)								*/
  /*			*NOTE: gain(i) & err(i) can be replaced by scalars		*/	
  l_codeword = 2*MAXNCSIZE - 2;
  cbindex = 1;
  gain[0] = cgain(&x[l_codeword], l, TRUE, LEN, &err[0]);
  emax = *err;
  l_codeword -= 2;
  for (i = 1; i < ncsize; i++)
  {
	gain[i] = cgain(&x[l_codeword], l, FALSE, LEN, &err[i]);
	l_codeword -= 2;
	if (err[i] >= emax)
	{
	  emax = err[i];
	  cbindex = i + 1;
	}
  }

  /*   if (err(cbindex).lt.0.0)print *,' CB match<0',frame,err(cbindex) */

  /*			*pointer to best code word								*/

  l_codeword = 2*(MAXNCSIZE - cbindex);

  /*			*OPTIONAL (may be useful for integer DSPs)				*/
  /*			*given best code word, recompute its gain to			*/
  /*			*correct any accumulated errors in recursions			*/
  gain[cbindex-1] = cgain(&x[l_codeword], l, TRUE, l, &err[cbindex-1]);

  oldgain = gain[cbindex - 1];

  /* *constrained excitation											*/
  if (mxsw) 
	mexcite3(&gain[cbindex - 1]);

  /*			*gain quantization, UNNECESSARY for closed-loop quant	*/
  
  if (strncmp(cbgtype, "none", 4) != 0) {
	if (cbgbits == 5) {
	  gain[cbindex-1] = gainencode(gain[cbindex-1], &gindex);
	} else {
#ifdef CELPDIAG
      fprintf(stderr, "cbsearch: not quantizing cbgain\n");
#endif
	}
  }
	
  /*			*scale selected code word vector -> excitation array	*/
  /*			*call VDECODE?											*/
  
  for (i = 0; i < l; i++)
	a_v[i] = gain[cbindex - 1] * x[i + l_codeword];
}
#undef LEN