quantize.asm

利用G.723协议在DSP实现音频信号的压缩与解压缩实验

;/*
; * quantize()
; *
; * Given a raw sample, 'd', of the difference signal and a
; * quantization step size scale factor, 'y', this routine returns the
; * ADPCM codeword to which that sample gets quantized.  The step
; * size scale factor division operation is done in the log base 2 domain
; * as a subtraction.
; */
;int
;quantize(
;	int		d,	/* Raw difference signal sample */
;	int		y,	/* Step size multiplier */
;	short		*table,	/* quantization table */
;	int		size)	/* table size of short integers */
;{
;	short		dqm;	/* Magnitude of 'd' */
;	short		exp;	/* Integer part of base 2 log of 'd' */
;	short		mant;	/* Fractional part of base 2 log */
;	short		dl;	/* Log of magnitude of 'd' */
;	short		dln;	/* Step size scale factor normalized log */
;	int		i;
;
;	/*
;	 * LOG
;	 *
;	 * Compute base 2 log of 'd', and store in 'dl'.
;	 */
;	dqm = abs(d);
;	exp = quan(dqm >> 1, power2, 15);
;	mant = ( dqm >> (exp-7) ) & 0x7F;	/* Fractional portion. */
;	dl = (exp << 7) + mant;
;---------------------------------

             .title   "quantize.asm"
             .include "g723_global.asm"
             .include "g723tab.asm"
             .include "g723_stat.asm"
             
             .mmregs
temp_dqm     .set       0
temp_yy      .set       1
             .text
            
           ;AR3=table, A=y, *AR6=d
quantize

        frame   #-2     
        ld	  *AR6, B
        stl   A, *SP(temp_yy)
        
        abs   B       ;B=dqm
        stl   B, *SP(temp_dqm)  
        sfta  B, -1  
        pshm  AR3
        stm   #power2, AR3 
        call  quan  ;B = dqm >> 1
                    ;AR3=power2
                    ;返回值exp=B
        popm  AR3
        sub   #7, B, A
        neg   A
        stlm  A, T
        ld    *SP(temp_dqm), A
        norm  A
        and   #0x7f, A    ;A=mant       
        add   B, 7, A     ;A=dl                                                                                                                    
;-------------------------------------------------
;	/*
;	 * SUBTB
;	 *
;	 * "Divide" by step size multiplier.
;	 */
;	dln = dl - (y >> 2);                       
;-------------------------------------------------
        ld    *SP(temp_yy), B
        sub   B, -2, A    ;A=dln
;-------------------------------------------------                                     
;	 * QUAN
;	 *
;	 * Obtain codword i for 'd'.
;	 */
;	i = quan(dln, table, size);
;	if (d < 0)			/* take 1's complement of i */
;		return ((size << 1) + 1 - i);
;	else if (i == 0)		/* take 1's complement of 0 */
;		return ((size << 1) + 1); /* new in 1988 */
;	else
;		return (i);
;-------------------------------------------------
        ld    A, B
        call  quan   ;B=dln, table=AR3
                     ;返回值 i=B
        ld    *AR6, A
        bc    ret_i, AGEQ
        ld     #15, 1, A
        add    #1, A
        sub    B, A
        frame  #2        
        ret  
ret_i         
        bc     ret_end, BNEQ             
        ld     #15, 1, A
        add    #1, A
        ;sub    B, A
        frame  #2
        ret          
ret_end 
        ld    B, A                               
        frame  #2
        ret
        
           .end