gaincode.c

语音CELP压缩解压源代码（C语音)

/**************************************************************************
*
* ROUTINE
*		gainencode
*
* FUNCTION
*
*		encode and quantize code book gain
*
* SYNOPSIS
*		subroutine gainencode(input, index)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	input		int	i	code book gain input (true value)
*	index		float	o	encoded code book gain ZERO BASED index
*	gainencode	float	func	encoded code book gain
*
***************************************************************************
*
* DESCRIPTION
*
*
*      Fast code book gain quantizer to allow practical quantization
*      inside the code book search loop. A binary tree search quantization 
*      is implemented below.
*
*
***************************************************************************
*
* CALLED BY
*
*	cbsearch cgain
*
* CALLS
*
*
***************************************************************************
*
* REFERENCES
*
*
**************************************************************************/
 /* *Log quantization                               */

static float gainlog5[32] =
{
 -1330., -870., -660., -520., -418., -340., -278., -224.,
 -178., -136.,  -98.,  -64.,  -35.,  -13.,   -3.,   -1.,
    1.,    3.,   13.,   35.,   64.,   98.,  136.,  178.,
  224.,  278.,  340.,  418.,  520.,  660.,  870., 1330.
};
#include <math.h>
float
gainencode(input, index)
float input;
int *index;

{
  int i;
  static float midpoints[31] = 
  {
    -1100., -765., -590., -469., -379., -309., -251., -201.,
     -157., -117.,  -81.,  -49.5, -24.,   -8.,   -2.,    0.,
        2.,    8.,   24.,   49.5,  81.,  117.,  157.,  201.,
      251.,  309.,  379.,  469.,  590.,  765., 1100.
  };

  /* *Binary tree search for closest gain				 */

  for (*index = 15, i = 8; i >= 1; i = i >> 1)
  {
    if (input > midpoints[*index])
      *index += i;
    else
      *index -= i;
  }
  if (input > midpoints[*index])
    (*index)++;

  /* *Return quantized gain and ZERO based index			 */

  return (gainlog5[*index]);
}
   

/**************************************************************************
*
* ROUTINE
*		gainencode2
*
* FUNCTION
*
*		encode and quantize code book gain
*
* SYNOPSIS
*		subroutine gainencode2(numer, denom, index)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	numer		int	i	code book gain numerator
*	denom		int	i	code book gain denominator
*	index		float	o	encoded code book gain ZERO BASED index
*	gainencode2	float	func	encoded code book gain
*
***************************************************************************
*
* DESCRIPTION
*
*
*     Fast nonuniform division for code book gain quantization to allow
*     practical quantization inside the code book search loop.  A binary
*     tree search with cross multiply quantization is implemented below.
*
*
*
***************************************************************************
*
* CALLED BY
*
*	cbsearch cgain
*
* CALLS
*
*
***************************************************************************
*
* REFERENCES
*
*
**************************************************************************/

float
gainencode2(numer, denom, index)
float numer, denom;
int *index;

{

  /* *Hard coded for 5 bit quantization to achieve high speed  	 	*/

  int i;
  static float midpoints[31] = 
  {
    -1100., -765., -590., -469., -379., -309., -251., -201.,
     -157., -117.,  -81.,  -49.5, -24.,   -8.,   -2.,    0.,
        2.,    8.,   24.,   49.5,  81.,  117.,  157.,  201.,
      251.,  309.,  379.,  469.,  590.,  765., 1100.
  };

  /* *Binary tree search for closest gain				 */

  for (*index = 15, i = 8; i >= 1; i = i >> 1)
  {
    if (numer  > denom * midpoints[*index])
      *index += i;
    else
      *index -= i;
  }
  if (numer > denom * midpoints[*index])
    (*index)++;

  /* *Return quantized gain and ZERO based index			 */

  return (gainlog5[*index]);
}
   


/**************************************************************************
*
* ROUTINE
*		gaindecode
*
* FUNCTION
*
*		decode code book gain from the gain index (gindex)
*		and bit index (bits).
*
* SYNOPSIS
*		subroutine gaindecode(gindex, bits, gain)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*	gindex		int	i	gain index value
*	bits		int	i	# bits for encode
*	gain		float	o	decoded code book gain value
*
***************************************************************************
*
* CALLED BY
*
*       dcodcbg	
*
* CALLS
*
*
***************************************************************************
*
* REFERENCES
*
*       Quantizing for Minimum Distorion
*       J. Max
*       IRE Trans. Inform. Theory, vol. IT-6, pp.7-12, Mar. 1960
*
***************************************************************************
*
*       The data used in the table generation is from 3m3f.spd.
*
**************************************************************************/
gaindecode(gindex, bits, gain)
int gindex, bits;
float *gain;

{
  /* Choose appropriate gain                                         */

  if (bits == 5)
    *gain = gainlog5[gindex];
  else
    printf("gaindecode: unquantized cbgain\n");
}