adpcm.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;

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

static 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
};
    

    
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 */

	LOG_printf(&trace, "Encode.c start:%d", CLK_gethtime());
	
    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+16;
	/* 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;
    }
    
    LOG_printf(&trace, "Encode.c end:%d", CLK_gethtime());
}

void decode(char *indata, short *outdata, int len, AdpcmState *state)
{
    signed char *inp;	/* Input buffer pointer */
    short *outp;		/* output buffer pointer */
    int sign;			/* Current adpcm sign bit */
    int delta;			/* Current adpcm output value */
    int step;			/* Stepsize */
    int valpred;		/* Predicted value */
    int vpdiff;			/* Current change to valpred */
    int index;			/* Current step change index */
    int inputbuffer;	/* place to keep next 4-bit value */
    int bufferstep;		/* toggle between inputbuffer/input */
    
    LOG_printf(&trace, "Decode.c start:%d", CLK_gethtime()); 

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

    valpred = state->valprev;
    index = state->index;
    step = stepsizeTable[index];

    bufferstep = 0;
    

    
    for ( ; len > 0 ; len-- ) 
    {
	
		/* Step 1 - get the delta value */
		if ( bufferstep ) {
		    delta = inputbuffer & 0xf;
		} else {
	    	inputbuffer = *inp++;
	    	delta = (inputbuffer >> 4) & 0xf;
		}
		
		

		/* Step 2 - Find new index value (for later) */
		index += indexTable[delta];
		if ( index < 0 ) index = 0;
		if ( index > 88 ) index = 88;

		/* Step 3 - Separate sign and magnitude */
		sign = delta & 8;
		delta = delta & 7;

	/* Step 4 - Compute difference and new predicted value */
	/*
	** Computes 'vpdiff = (delta+0.5)*step/4', but see comment
	** in adpcm_coder.
	*/
		vpdiff = step >> 3;
		if ( delta & 4 ) vpdiff += step;
		if ( delta & 2 ) vpdiff += step>>1;
		if ( delta & 1 ) vpdiff += step>>2;

		if ( sign )
	  	valpred -= vpdiff;
		else
	  	valpred += vpdiff;

		/* Step 5 - clamp output value */
		if ( valpred > 32767 )
	  		valpred = 32767;
		else if ( valpred < -32768 )
	  	valpred = -32768;

		/* Step 6 - Update step value */
		step = stepsizeTable[index];

		/* Step 7 - Output value */
			*outp = valpred;
			outp=outp+16;
  	
		    
    	bufferstep = !bufferstep;
    }

    state->valprev = valpred;
    state->index = index;
 
    //write to file
    //fwrite(outdata, 1, len, fpDecoder);
    LOG_printf(&trace, "Decode.c end:%d", CLK_gethtime());
}