g721.c

DM642平台上的H.264源码(可实时运行)

/*
 * g721.c
 *
 * Description:
 *
 * g721_encoder(), g721_decoder()
 *
 * These routines comprise an implementation of the CCITT G.721 ADPCM
 * coding algorithm.  Essentially, this implementation is identical to
 * the bit level description except for a few deviations which
 * take advantage of work station attributes, such as hardware 2's
 * complement arithmetic and large memory.  Specifically, certain time
 * consuming operations such as multiplications are replaced
 * with lookup tables and software 2's complement operations are
 * replaced with hardware 2's complement.
 *
 * The deviation from the bit level specification (lookup tables)
 * preserves the bit level performance specifications.
 *
 * As outlined in the G.721 Recommendation, the algorithm is broken
 * down into modules.  Each section of code below is preceded by
 * the name of the module which it is implementing.
 *
 */
#include "g72x.h"

static short qtab_721[7] = {-124, 80, 178, 246, 300, 349, 400};
/*
 * Maps G.721 code word to reconstructed scale factor normalized log
 * magnitude values.
 */
static short	_dqlntab[16] = {-2048, 4, 135, 213, 273, 323, 373, 425,
				425, 373, 323, 273, 213, 135, 4, -2048};

/* Maps G.721 code word to log of scale factor multiplier. */
static short	_witab[16] = {-12, 18, 41, 64, 112, 198, 355, 1122,
				1122, 355, 198, 112, 64, 41, 18, -12};


/*
 * g721_encoder()
 *
 * Encodes the input vale of linear PCM, A-law or u-law data sl and returns
 * the resulting code. -1 is returned for unknown input coding value.
 */
short
g721_encoder(
	short		sl,
	struct g72x_state *state_ptr)
{
	short		sezi, se, sez;		/* ACCUM */
	short		d;			/* SUBTA */
	short		sr;			/* ADDB */
	short		y;			/* MIX */
	short		dqsez;			/* ADDC */
	short		dq, i;

	sl >>=2;			/* 14-bit dynamic range */
	sezi = predictor_zero(state_ptr);
	sez = sezi >> 1;
	se = (sezi + predictor_pole(state_ptr)) >> 1;	/* estimated signal */

	d = sl - se;				/* estimation difference */

	/* quantize the prediction difference */
	y = state_ptr->yu;		/* quantizer step size */
	i = quantize(d, y, qtab_721, 7);	/* i = ADPCM code */

	dq = reconstruct(i & 8, _dqlntab[i], y);	/* quantized est diff */

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

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

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

	return (i);
}

/*
 * g721_decoder()
 *
 * Description:
 *
 * Decodes a 4-bit code of G.721 encoded data of i and
 * returns the resulting linear PCM, A-law or u-law value.
 * return -1 for unknown out_coding value.
 */
short
g721_decoder(
	short		i,
	struct g72x_state *state_ptr)
{
	short		sezi, sei, sez, se;	/* ACCUM */
	short		y;			/* MIX */
	short		sr;			/* ADDB */
	short		dq;
	short		dqsez;

	i &= 0x0f;			/* mask to get proper bits */
	sezi = predictor_zero(state_ptr);
	sez = sezi >> 1;
	sei = sezi + predictor_pole(state_ptr);
	se = sei >> 1;			/* se = estimated signal */

	y = state_ptr->yu;	/* dynamic quantizer step size */

	dq = reconstruct(i & 0x08, _dqlntab[i], y); /* quantized diff. */

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

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

	update( y, _witab[i], dq, sr, dqsez, state_ptr);
		
	return (sr<<2) ;	/* sr was 14-bit dynamic range */

}

/*
 * Pack output codes into bytes and write them to stdout.
 * Returns 1 if there is residual output, else returns 0.
 */
void pack_output(short *in_code,unsigned short *out_byte,int len)
{
	int i;
	unsigned short code;
	static unsigned short out_buffer = 0;
	static int		out_bits = 0;

	for(i=0;i<len;i++)
	{
		code=in_code[i]&0x0f;
		out_buffer |= (code << out_bits);
		out_bits += 4;
		if (out_bits >= 16) {
			*out_byte++ = out_buffer;
			out_bits = 0;
			out_buffer = 0;
		}
		
	}
	if(out_bits >0){
		*out_byte = out_buffer;
		out_bits = 0;
		out_buffer = 0;
	}
}

/*
 * Unpack input codes and pass them back as bytes.
 * Returns 1 if there is residual input, returns -1 if eof, else returns 0.
 */
void unpack_input(unsigned short *in_byte,short *out_code,int len)
{
	int i;
	static unsigned short	in_buffer = 0;
	static int		in_bits = 0;
	
	for(i=0;i<len;i++){	
		if (in_bits < 4) {
			in_buffer = *in_byte++;
			in_bits += 16;
		}
		*out_code++ = in_buffer & 0x0f;
		in_buffer >>= 4;
		in_bits -= 4;
	}
	
}