g.723_24_encoder.cpp

g.723_24的整理函数

/* g723_24_encoder()
 * Encodes a linear PCM sample and returns its 3-bit code.

when you use the function you should include:

#include <G72x.c>   
#include <G72x.h>   //declare the function that transfered 
*/

int
g723_24_encoder(
	int		sl)
{
	struct g72x_state *state_ptr;
	int		cnta;

	state_ptr->yl = 34816;
	state_ptr->yu = 544;
	state_ptr->dms = 0;
	state_ptr->dml = 0;
	state_ptr->ap = 0;
	for (cnta = 0; cnta < 2; cnta++) {
		state_ptr->a[cnta] = 0;
		state_ptr->pk[cnta] = 0;
		state_ptr->sr[cnta] = 32;
	}
	for (cnta = 0; cnta < 6; cnta++) {
		state_ptr->b[cnta] = 0;
		state_ptr->dq[cnta] = 32;
	}
	state_ptr->td = 0;

	short		sezi, sei, sez, se;	/* ACCUM */
	short		y;			/* MIX */
	short		sr;			/* ADDB */
	short		dq;
	short		dqsez;
	short		dq, i;
	
	
static short	_dqlntab[8] = {-2048, 135, 273, 373, 373, 273, 135, -2048};
static short	_witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};
static short	_fitab[8] = {0, 0x200, 0x400, 0xE00, 0xE00, 0x400, 0x200, 0};
static short qtab_723_24[3] = {8, 218, 331};
static short power2[15] = {1, 2, 4, 8, 0x10, 0x20, 0x40, 0x80,
			0x100, 0x200, 0x400, 0x800, 0x1000, 0x2000, 0x4000};
			
	sl >>= 2;		
			
	sezi = predictor_zero(state_ptr);
	sez = sezi >> 1;
	sei = sezi + predictor_pole(state_ptr);
	se = sei >> 1;			/* se = estimated signal */

	d = sl - se;			/* d = estimation diff. */

	/* quantize prediction difference d */
	y = step_size(state_ptr);	/* quantizer step size */
	i = quantize(d, y, qtab_723_24, 3);	/* i = ADPCM code */
	dq = reconstruct(i & 4, _dqlntab[i], y); /* quantized diff. */

	sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */

	dqsez = sr + sez - se;		/* pole prediction diff. */

	update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

	return (i);
}