www.pudn.com > CryptoPhone-src-031122.zip > scb_code.c

/* Copyright 2001,2002,2003 NAH6 
 * All Rights Reserved 
 * 
 * Parts Copyright DoD, Parts Copyright Starium 
 * 
 */ 
          /*LINTLIBRARY*/ 
          /*PROTOLIB1*/ 
#include  
#include "main.h" 
#include "scb_code.h" 
 
/************************************************************************** 
* 
* ROUTINE 
*		SCBGainEncode 
* 
* FUNCTION 
* 
*		encode and quantize code book gain 
* 
* SYNOPSIS 
*		SCBGainEncode(UGain, QGain) 
* 
*   formal 
* 
*                       data    I/O 
*       name            type    type    function 
*       ------------------------------------------------------------------- 
*	UGain		float	i	code book gain input (true value) 
*	QGain		int	o	encoded code book gain ZERO BASED index 
* 
*	SCBGainEncode	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. 
* 
**************************************************************************/ 
  
/* *Log quantization                               */ 
 
static float SCBGainTable[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. 
}; 
 
float SCBGainEncode( 
float 	UGain, 
int 	*QGain) 
 
{ 
  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 (*QGain = 15, i = 8; i >= 1; i = i >> 1) 
  { 
    if (UGain > midpoints[*QGain]) 
      *QGain += i; 
    else 
      *QGain -= i; 
  } 
  if (UGain > midpoints[*QGain]) 
    (*QGain)++; 
 
  /* *Return quantized gain and ZERO based index			 */ 
 
  return (SCBGainTable[*QGain]); 
} 
    
 
/* 
 
************************************************************************* 
* 
* ROUTINE 
*		SCBGainDecode 
* 
* FUNCTION 
* 
*		decode code book gain from the quantized gain  
* 
* SYNOPSIS 
*		SCBGainDecode(QGain, UGain) 
* 
*   formal 
* 
*                       data    I/O 
*       name            type    type    function 
*       ------------------------------------------------------------------- 
*	QGain		int	i	Quantized gain 
*	UGain		float	o	Unquantized gain 
* 
*************************************************************************** 
* 
* 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. 
* 
**************************************************************************/ 
void SCBGainDecode( 
int 	QGain,  
float 	*UGain) 
 
{ 
  /* Choose appropriate gain                                         */ 
 
    *UGain = SCBGainTable[QGain]; 
 
}