simple_idct.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
 *  - Inverse DCT (More precise version)  -
 *
 *  Copyright (c) 2001 Michael Niedermayer <[e-mail]>
 *
 *  Originally distributed under the GNU LGPL License (ffmpeg).
 *  It is licensed under the GNU GPL for the XviD tree.
 *
 *  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: simple_idct.c,v 1.5 2004/04/05 20:36:36 edgomez Exp $
 *
 ****************************************************************************/

/*
  based upon some outcommented c code from mpeg2dec (idct_mmx.c
  written by Aaron Holtzman <[e-mail]>)
 */

#include "../portab.h"
#include "idct.h"

#if 0
#define W1 2841 /* 2048*sqrt (2)*cos (1*pi/16) */
#define W2 2676 /* 2048*sqrt (2)*cos (2*pi/16) */
#define W3 2408 /* 2048*sqrt (2)*cos (3*pi/16) */
#define W4 2048 /* 2048*sqrt (2)*cos (4*pi/16) */
#define W5 1609 /* 2048*sqrt (2)*cos (5*pi/16) */
#define W6 1108 /* 2048*sqrt (2)*cos (6*pi/16) */
#define W7 565  /* 2048*sqrt (2)*cos (7*pi/16) */
#define ROW_SHIFT 8
#define COL_SHIFT 17
#else
#define W1  22725  /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W2  21407  /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W3  19266  /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W4  16383  /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W5  12873  /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W6  8867   /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define W7  4520   /* cos(i*M_PI/16)*sqrt(2)*(1<<14) + 0.5 */
#define ROW_SHIFT 11
#define COL_SHIFT 20 /* 6 */
#endif

/*
 PPC mac operation.  Causes compile problems on newer ppc targets
 
 Was originally: #if defined(ARCH_IS_PPC)
 */
#if 0

/* signed 16x16 -> 32 multiply add accumulate */
#define MAC16(rt, ra, rb) \
    asm ("maclhw %0, %2, %3" : "=r" (rt) : "0" (rt), "r" (ra), "r" (rb));

/* signed 16x16 -> 32 multiply */
#define MUL16(rt, ra, rb) \
    asm ("mullhw %0, %1, %2" : "=r" (rt) : "r" (ra), "r" (rb));

#else

/* signed 16x16 -> 32 multiply add accumulate */
#define MAC16(rt, ra, rb) rt += (ra) * (rb)

/* signed 16x16 -> 32 multiply */
#define MUL16(rt, ra, rb) rt = (ra) * (rb)

#endif

static __inline void idctRowCondDC (int16_t * const row)
{
	int a0, a1, a2, a3, b0, b1, b2, b3;
#ifdef FAST_64BIT
        uint64_t temp;
#else
        uint32_t temp;
#endif

#ifdef FAST_64BIT
#ifdef ARCH_IS_BIG_ENDIAN
#define ROW0_MASK 0xffff000000000000LL
#else
#define ROW0_MASK 0xffffLL
#endif
	if ( ((((uint64_t *)row)[0] & ~ROW0_MASK) |
              ((uint64_t *)row)[1]) == 0) {
            temp = (row[0] << 3) & 0xffff;
            temp += temp << 16;
            temp += temp << 32;
            ((uint64_t *)row)[0] = temp;
            ((uint64_t *)row)[1] = temp;
            return;
	}
#else
	if (!(((uint32_t*)row)[1] |
              ((uint32_t*)row)[2] |
              ((uint32_t*)row)[3] |
              row[1])) {
            temp = (row[0] << 3) & 0xffff;
            temp += temp << 16;
            ((uint32_t*)row)[0]=((uint32_t*)row)[1] =
		((uint32_t*)row)[2]=((uint32_t*)row)[3] = temp;
		return;
	}
#endif

        a0 = (W4 * row[0]) + (1 << (ROW_SHIFT - 1));
	a1 = a0;
	a2 = a0;
	a3 = a0;

        /* no need to optimize : gcc does it */
        a0 += W2 * row[2];
        a1 += W6 * row[2];
        a2 -= W6 * row[2];
        a3 -= W2 * row[2];

        MUL16(b0, W1, row[1]);
        MAC16(b0, W3, row[3]);
        MUL16(b1, W3, row[1]);
        MAC16(b1, -W7, row[3]);
        MUL16(b2, W5, row[1]);
        MAC16(b2, -W1, row[3]);
        MUL16(b3, W7, row[1]);
        MAC16(b3, -W5, row[3]);

#ifdef FAST_64BIT
        temp = ((uint64_t*)row)[1];
#else
        temp = ((uint32_t*)row)[2] | ((uint32_t*)row)[3];
#endif
	if (temp != 0) {
            a0 += W4*row[4] + W6*row[6];
            a1 += - W4*row[4] - W2*row[6];
            a2 += - W4*row[4] + W2*row[6];
            a3 += W4*row[4] - W6*row[6];

            MAC16(b0, W5, row[5]);
            MAC16(b0, W7, row[7]);

            MAC16(b1, -W1, row[5]);
            MAC16(b1, -W5, row[7]);

            MAC16(b2, W7, row[5]);
            MAC16(b2, W3, row[7]);

            MAC16(b3, W3, row[5]);
            MAC16(b3, -W1, row[7]);
	}

	row[0] = (a0 + b0) >> ROW_SHIFT;
	row[7] = (a0 - b0) >> ROW_SHIFT;
	row[1] = (a1 + b1) >> ROW_SHIFT;
	row[6] = (a1 - b1) >> ROW_SHIFT;
	row[2] = (a2 + b2) >> ROW_SHIFT;
	row[5] = (a2 - b2) >> ROW_SHIFT;
	row[3] = (a3 + b3) >> ROW_SHIFT;
	row[4] = (a3 - b3) >> ROW_SHIFT;
}


static __inline void idctSparseCol (int16_t * const col)
{
	int a0, a1, a2, a3, b0, b1, b2, b3;

        /* XXX: I did that only to give same values as previous code */
	a0 = W4 * (col[8*0] + ((1<<(COL_SHIFT-1))/W4));
	a1 = a0;
	a2 = a0;
	a3 = a0;

        a0 +=  + W2*col[8*2];
        a1 +=  + W6*col[8*2];
        a2 +=  - W6*col[8*2];
        a3 +=  - W2*col[8*2];

        MUL16(b0, W1, col[8*1]);
        MUL16(b1, W3, col[8*1]);
        MUL16(b2, W5, col[8*1]);
        MUL16(b3, W7, col[8*1]);

        MAC16(b0, + W3, col[8*3]);
        MAC16(b1, - W7, col[8*3]);
        MAC16(b2, - W1, col[8*3]);
        MAC16(b3, - W5, col[8*3]);

	if(col[8*4]){
            a0 += + W4*col[8*4];
            a1 += - W4*col[8*4];
            a2 += - W4*col[8*4];
            a3 += + W4*col[8*4];
	}

	if (col[8*5]) {
            MAC16(b0, + W5, col[8*5]);
            MAC16(b1, - W1, col[8*5]);
            MAC16(b2, + W7, col[8*5]);
            MAC16(b3, + W3, col[8*5]);
	}

	if(col[8*6]){
            a0 += + W6*col[8*6];
            a1 += - W2*col[8*6];
            a2 += + W2*col[8*6];
            a3 += - W6*col[8*6];
	}

	if (col[8*7]) {
            MAC16(b0, + W7, col[8*7]);
            MAC16(b1, - W5, col[8*7]);
            MAC16(b2, + W3, col[8*7]);
            MAC16(b3, - W1, col[8*7]);
	}

        col[0 ] = ((a0 + b0) >> COL_SHIFT);
        col[8 ] = ((a1 + b1) >> COL_SHIFT);
        col[16] = ((a2 + b2) >> COL_SHIFT);
        col[24] = ((a3 + b3) >> COL_SHIFT);
        col[32] = ((a3 - b3) >> COL_SHIFT);
        col[40] = ((a2 - b2) >> COL_SHIFT);
        col[48] = ((a1 - b1) >> COL_SHIFT);
        col[56] = ((a0 - b0) >> COL_SHIFT);
}

void simple_idct_c(int16_t * const block)
{
    int i;
    for(i=0; i<8; i++)
        idctRowCondDC(block + i*8);

    for(i=0; i<8; i++)
        idctSparseCol(block + i);
}