cbp.c

这是一个压缩解压包,用C语言进行编程的,里面有详细的源代码.

/*****************************************************************************
 *
 *  XVID MPEG-4 VIDEO CODEC
 *  - CBP related function  -
 *
 *  Copyright(C) 2002-2003 Edouard Gomez <[e-mail]>
 *               2003      Christoph Lampert <[e-mail]>
 *
 *  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 * $Id: cbp.c,v 1.13 2004/03/22 22:36:23 edgomez Exp $
 *
 ****************************************************************************/

#include "../portab.h"
#include "cbp.h"

cbpFuncPtr calc_cbp;

/*
 * Returns a field of bits that indicates non zero ac blocks
 * for this macro block
 */

/* naive C */
uint32_t
calc_cbp_plain(const int16_t codes[6 * 64])
{
	int i, j;
	uint32_t cbp = 0;

	for (i = 0; i < 6; i++) {
		for (j=1; j<64;j++) {
			if (codes[64*i+j]) {
            	cbp |= 1 << (5-i);
				break;
			}
		}
	}
	return cbp;
}

/* optimized C */
uint32_t
calc_cbp_c(const int16_t codes[6 * 64])
{
	unsigned int i=6;
	uint32_t cbp = 0;

/* uses fixed relation: 4*codes = 1*codes64 */
/* if prototype is changed (e.g. from int16_t to something like int32) this routine
   has to be changed! */

	do  {
		uint64_t *codes64 = (uint64_t*)codes;	/* the compiler doesn't really make this */
		uint32_t *codes32 = (uint32_t*)codes;	/* variables, just "addressing modes" */

		cbp += cbp;
        if (codes[1] || codes32[1]) {
			cbp++;
		}
        else if (codes64[1] | codes64[2] | codes64[3]) {
			cbp++;
		}
        else if (codes64[4] | codes64[5] | codes64[6] | codes64[7]) {
			cbp++;
		}
        else if (codes64[8] | codes64[9] | codes64[10] | codes64[11]) {
			cbp++;
		}
        else if (codes64[12] | codes64[13] | codes64[14] | codes64[15]) {
			cbp++;
		}
		codes += 64;
		i--;
    } while (i != 0);

	return cbp;
}




/* older code maybe better on some plattforms? */
#if 0
	for (i = 5; i >= 0; i--) {
		if (codes[1] | codes[2] | codes[3])
                        cbp |= 1 << i;
		else {
			for (j = 4; j <= 56; j+=4) 	/* [60],[61],[62],[63] are last */
				if (codes[j] | codes[j+1] | codes[j+2] | codes[j+3]) {
				cbp |= 1 << i;
				break;
			}
		}
		codes += 64;
	}

	return cbp;
#endif