enc.c

基于TI xdais算法标准的音频ADPCM算法

#include <stdio.h>
#include "adpcm.h"
#include "evmdm642_echocfg.h"


#ifndef __STDC__
#define signed
#endif

extern far LOG_Obj trace;
extern far int stepsizeTable[];
extern far int indexTable[];

void encode(short *indata, char *outdata, int len, AdpcmState *state)
{
    short *inp;			/* Input buffer pointer */
    signed char *outp;	/* output buffer pointer */
    //int val;			/* Current input sample value*/
    short val;
    int sign;			/* Current adpcm sign bit */
    int delta;			/* Current adpcm output value */
    int diff;			/* Difference between val and valprev */
    int step;			/* Stepsize*/
    //int valpred;		/* Predicted output value */
    short valpred;
    int vpdiff;			/* Current change to valpred */
    int index;			/* Current step change index */
    int outputbuffer;	/* place to keep previous 4-bit value */
    int bufferstep;		/* toggle between outputbuffer/output */

    outp = (signed char *)outdata;
    inp = indata;

    valpred = state->valprev;
    index = state->index;
    step = stepsizeTable[index];/*step=stepsizeTable[index]*/
    
    bufferstep = 1;

    for ( ; len > 0 ; len-- ) {
    {
			val = *inp;
			inp=inp+32;
	/* Step 1 - compute difference with previous value */
		diff = val - valpred;
		sign = (diff < 0) ? 8 : 0;
		if ( sign ) diff = (-diff);

	/* Step 2 - Divide and clamp */
	/* Note:
	** This code *approximately* computes:
	**    delta = diff*4/step;
	**    vpdiff = (delta+0.5)*step/4;
	** but in shift step bits are dropped. 
	** The net result of this is
	** that even if you have fast mul/div hardware you cannot put it to
	** good use since the fixup would be too expensive.
	*/
		delta = 0;
		vpdiff = (step >> 3);
	
		if ( diff >= step ) {
	    	delta = 4;
	    	diff -= step;
	    	vpdiff += step;
		}
		step >>= 1;
		if ( diff >= step  ) {
	    	delta |= 2;
	    	diff -= step;
	    	vpdiff += step;
		}
		step >>= 1;
		if ( diff >= step ) {
	    	delta |= 1;
	    	vpdiff += step;
		}

	/* Step 3 - Update previous value */
		if ( sign )
	  		valpred -= vpdiff;
		else
	  		valpred += vpdiff;

	/* Step 4 - Clamp previous value to 16 bits */
		if ( valpred > 32767 )
	  	  	valpred = 32767;
		else if ( valpred < -32768 )
		  	valpred = -32768;

	/* Step 5 - Assemble value, update index and step values */
		delta |= sign;
	
			index += indexTable[delta];
			if ( index < 0 ) index = 0;
			if ( index > 88 ) index = 88;
			step = stepsizeTable[index];

	/* Step 6 - Output value */
			if ( bufferstep ) 
			  {
	    	     outputbuffer = (delta << 4) & 0xf0;
			  } 
			else 
			  {
	    		 *outp++ = (delta & 0x0f) | outputbuffer;
			  }
			
			bufferstep = !bufferstep;
    }

    /* Output last step, if needed */
    /*if ( !bufferstep )
      *outp++ = outputbuffer;*/
    
    	state->valprev = valpred;
    	state->index = index;
    }
    
}