quant_h263.c

MPEG-4编解码的实现(包括MPEG4视音频编解码)

/**************************************************************************
 *
 *	XVID MPEG-4 VIDEO CODEC
 *	quantization/dequantization
 *
 *	This program is an implementation of a part of one or more MPEG-4
 *	Video tools as specified in ISO/IEC 14496-2 standard.  Those intending
 *	to use this software module in hardware or software products are
 *	advised that its use may infringe existing patents or copyrights, and
 *	any such use would be at such party's own risk.  The original
 *	developer of this software module and his/her company, and subsequent
 *	editors and their companies, will have no liability for use of this
 *	software or modifications or derivatives thereof.
 *
 *	This program is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU General Public License as published by
 *	the Free Software Foundation; either version 2 of the License, or
 *	(at your option) any later version.
 *
 *	This program is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU General Public License for more details.
 *
 *	You should have received a copy of the GNU General Public License
 *	along with this program; if not, write to the Free Software
 *	Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 *************************************************************************/

/**************************************************************************
 *
 *	History:
 *
 *  26.12.2001	dequant_inter bug fix
 *	22.12.2001	clamp dequant output to [-2048,2047]
 *  19.11.2001  quant_inter now returns sum of abs. coefficient values
 *	02.11.2001	added const to function args <[e-mail]>
 *	28.10.2001	total rewrite <[e-mail]>
 *
 *************************************************************************/

#include "quant_h263.h"

/*	mutliply+shift division table
*/

#define SCALEBITS	16
#define FIX(X)		((1L << SCALEBITS) / (X) + 1)

static const uint32_t multipliers[32] =
{
	0,			FIX(2),		FIX(4),		FIX(6),
	FIX(8),		FIX(10),	FIX(12),	FIX(14),
	FIX(16),	FIX(18),	FIX(20),	FIX(22),
	FIX(24),	FIX(26),	FIX(28),	FIX(30),
	FIX(32),	FIX(34),	FIX(36),	FIX(38),
	FIX(40),	FIX(42),	FIX(44),	FIX(46),
	FIX(48),	FIX(50),	FIX(52),	FIX(54),
	FIX(56),	FIX(58),	FIX(60),	FIX(62)
}; 



#define DIV_DIV(a, b) ((a)>0) ? ((a)+((b)>>1))/(b) : ((a)-((b)>>1))/(b)

// function pointers
quanth263_intraFuncPtr quant_intra;
quanth263_intraFuncPtr dequant_intra;

quanth263_interFuncPtr quant_inter;
dequanth263_interFuncPtr dequant_inter;



/*	quantize intra-block
*/


void quant_intra_c(int16_t * coeff, const int16_t * data, const uint32_t quant, const uint32_t dcscalar)
{
	const uint32_t mult = multipliers[quant];
	const uint16_t quant_m_2 = quant << 1;
    uint32_t i;

	coeff[0] = DIV_DIV(data[0], (int32_t)dcscalar);

	for (i = 1; i < 64; i++) {
		int16_t acLevel = data[i];

		if (acLevel < 0) {
			acLevel = -acLevel;
			if (acLevel < quant_m_2) {
				coeff[i] = 0;
				continue;
			}
			acLevel = (acLevel * mult) >> SCALEBITS;
			coeff[i] = -acLevel;
		} else {
			if (acLevel < quant_m_2) {
				coeff[i] = 0;
				continue;
			}
			acLevel = (acLevel * mult) >> SCALEBITS;
			coeff[i] = acLevel;
		}
	}
}


/*	quantize inter-block
*/

uint32_t quant_inter_c(int16_t *coeff, const int16_t *data, const uint32_t quant)
{
	const uint32_t mult = multipliers[quant];
	const uint16_t quant_m_2 = quant << 1;
	const uint16_t quant_d_2 = quant >> 1;
	int sum = 0;
	uint32_t i;

	for (i = 0; i < 64; i++) {
		int16_t acLevel = data[i];
		
		if (acLevel < 0) {
			acLevel = (-acLevel) - quant_d_2;
			if (acLevel < quant_m_2) {
				coeff[i] = 0;
				continue;
			}

			acLevel = (acLevel * mult) >> SCALEBITS;
			sum += acLevel;		// sum += |acLevel|
			coeff[i] = -acLevel;
		} else {
			acLevel -= quant_d_2;
			if (acLevel < quant_m_2) {
				coeff[i] = 0;
				continue;
			}
			acLevel = (acLevel * mult) >> SCALEBITS;
			sum += acLevel;
			coeff[i] = acLevel;
		}
	}

	return sum;
}


/*	dequantize intra-block & clamp to [-2048,2047]
*/

void dequant_intra_c(int16_t *data, const int16_t *coeff, const uint32_t quant, const uint32_t dcscalar)
{
	const int32_t quant_m_2 = quant << 1;
	const int32_t quant_add = (quant & 1 ? quant : quant - 1);
    uint32_t i;

	data[0] = coeff[0]  * dcscalar;
	if (data[0] < -2048)
	{
		data[0] = -2048;
	} 
	else if (data[0] > 2047)
	{
		data[0] = 2047;
	}


	for (i = 1; i < 64; i++) {
		int32_t acLevel = coeff[i];
		if (acLevel == 0)
		{
			data[i] = 0;
		} 
		else if (acLevel < 0) 
		{
			acLevel = quant_m_2 * -acLevel + quant_add;
			data[i] = (acLevel <= 2048 ? -acLevel : -2048);
		} 
		else  //  if (acLevel > 0) {
		{   
			acLevel = quant_m_2 * acLevel + quant_add;
			data[i] = (acLevel <= 2047 ? acLevel : 2047);
		}
	}
}



/* dequantize inter-block & clamp to [-2048,2047]
*/

void dequant_inter_c(int16_t *data, const int16_t *coeff, const uint32_t quant)
{
	const uint16_t quant_m_2 = quant << 1;
	const uint16_t quant_add = (quant & 1 ? quant : quant - 1);
	uint32_t i;

	for (i = 0; i < 64; i++) {
		int16_t acLevel = coeff[i];
		
		if (acLevel == 0)
		{
			data[i] = 0;
		}
		else if (acLevel < 0) 
		{
			acLevel = acLevel * quant_m_2 - quant_add;
			data[i] = (acLevel >= -2048 ? acLevel : -2048);
		} 
		else // if (acLevel > 0)
		{ 
			acLevel = acLevel * quant_m_2 + quant_add;
			data[i] = (acLevel <= 2047 ? acLevel : 2047);
		}
	}
}