my_ima.h

这是一个基于TI的DSP的ADPCM的源代码,经过测试.

extern int SavePCMTempWp;
#define SavePCMTempSize1 505+220
extern int LeftNum;

#define FrameSize 505
/* Intel ADPCM step variation table */
int indexTable[16] = {
    -1, -1, -1, -1, 2, 4, 6, 8,
    -1, -1, -1, -1, 2, 4, 6, 8,
};

int stepsizeTable[89] = {
    7, 8, 9, 10, 11, 12, 13, 14, 16, 17,
    19, 21, 23, 25, 28, 31, 34, 37, 41, 45,
    50, 55, 60, 66, 73, 80, 88, 97, 107, 118,
    130, 143, 157, 173, 190, 209, 230, 253, 279, 307,
    337, 371, 408, 449, 494, 544, 598, 658, 724, 796,
    876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066,
    2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358,
    5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
    15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767
};

int code_valprev,code_index;

void Adpcm_init(void)
{
 code_valprev=0;
 code_index=0;
}

void adpcm_coder(int *inp,int *outp,int len)
{
    int val;			/* Current input sample value */
    long delta;			/* Current adpcm output value */
    int step;			/* Stepsize */
    long valprev;		/* virtual previous output value */
    int index;			/* Current step change index */
    int  i=0;
    int SampXCode;
    int Sample0;
    unsigned int outtemp[3],outindex=0;
    
    Sample0=*(inp++);
    /*the first sample*/
    valprev = Sample0;
    /*previous output value*/
    index = code_index;
      
    *(outp++)=Sample0;// save sample0
    *(outp++)=index;
    len--;
    for(i=0;i<len;i++)  
     {
	   val =*(inp++);
	   step = stepsizeTable[index];
  	   /* Step 1 - compute difference with previous value */
	   delta = val - valprev;
	   if(delta<0)
	     {SampXCode=8;
	      delta=-delta;}
	     else SampXCode=0;
	   if(delta>=step)
	      {SampXCode=SampXCode|4;
	       delta=delta-step;
	       }     
	   if(delta>=(step>>1))
	      {SampXCode=SampXCode|2;
	       delta=delta-(step>>1);
	       }          
	   if(delta>=(step>>2))SampXCode=SampXCode|1;

      //预测采样值
	   delta=0;   	  
	   if(SampXCode&4)delta=delta+step;
	   if(SampXCode&2)delta=delta+(step>>1);        
	   if(SampXCode&1)delta=delta+(step>>2);
	   delta=delta+(step>>3); 	
	   if(SampXCode&8)delta=-delta;
	   
	   valprev+=delta;  
	   if ( valprev > 32767 )valprev = 32767;
           	else if ( valprev < -32768 ) valprev = -32768;
	   
	   index += indexTable[SampXCode];
	   if ( index < 0 ) index = 0;
	   if ( index > 88 ) index = 88;
        if(outindex<3)outtemp[outindex++]=SampXCode;
	      else {
	      *(outp++)=(SampXCode<<12)|(outtemp[2]<<8)|(outtemp[1]<<4)|outtemp[0]; 
             outindex=0; 
  	         }
	}     

	  
  //code_valprev =  valprev;
  code_index   =  index;
}

long adpcm_decoder(int *inp,int *outp,int len)
{
    long delta,c;			/* Current adpcm output value */
    int  step;			/* Stepsize */
    long valprev;		/* virtual previous output value */
    int  index;
    int i,j;			/* Current step change index */
    unsigned int SampXCode;
    unsigned int temp[4];
    long Energy;
     
    *(outp+SavePCMTempWp++)=*inp;
    SavePCMTempWp%=SavePCMTempSize1;
    valprev =(int) *(inp++); 
    Energy=abs(valprev);
    
    index = *(inp++)&0x00ff;  
      
    for(i=0;i<len;i++)  
     {/* Step 1 - get the delta value and compute next index */
      SampXCode = *(inp++);
      temp[3]= SampXCode>>12;
      temp[2]= (SampXCode>>8)&0x000f;
      temp[1]= (SampXCode>>4)&0x000f;
      temp[0]= SampXCode&0x000f;
      for(j=0;j<4;j++)  
       {    
        SampXCode = temp[j];
        delta=0;
        c= SampXCode&0x07;
        step = stepsizeTable[index];    
        delta=((c+c+1)*step)>>3; 	
	    if(SampXCode&8)delta=-delta;
	   
	    valprev+=delta; 
	    if ( valprev > 32767 )valprev=32767;
          	else if ( valprev < -37680 )valprev-=-32768;
          	
        index += indexTable[SampXCode];
	    if ( index < 0 ) index = 0;
	    if ( index > 88 ) index = 88;    	
        *(outp+SavePCMTempWp++)=(int)valprev;
        SavePCMTempWp%=SavePCMTempSize1;
        Energy=Energy+abs(valprev);
       } 
    }
 LeftNum+=505;   
 return(Energy) ;  
}