idct.c

网络MPEG4IP流媒体开发源代码

#include "idct.h"
#include <stdlib.h>

/**********************************************************/
/* inverse two dimensional DCT, Chen-Wang algorithm       */
/* (cf. IEEE ASSP-32, pp. 803-816, Aug. 1984)             */
/* 32-bit integer arithmetic (8 bit coefficients)         */
/* 11 mults, 29 adds per DCT                              */
/*                                      sE, 18.8.91       */
/**********************************************************/
/* coefficients extended to 12 bit for IEEE1180-1990      */
/* compliance                           sE,  2.1.94       */
/**********************************************************/

/* this code assumes >> to be a two's-complement arithmetic */
/* right shift: (-2)>>1 == -1 , (-3)>>1 == -2               */

#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 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) */

/* row (horizontal) IDCT
 *
 *           7                       pi         1
 * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l )
 *          l=0                      8          2
 *
 * where: c[0]    = 128
 *        c[1..7] = 128*sqrt(2)
 */

int mpeg3video_idctrow(short *blk)
{
	int x0, x1, x2, x3, x4, x5, x6, x7, x8;

	/* shortcut */
	if (!((x1 = blk[4]<<11) | (x2 = blk[6]) | (x3 = blk[2]) |
          (x4 = blk[1]) | (x5 = blk[7]) | (x6 = blk[5]) | (x7 = blk[3])))
	{
      blk[0]=blk[1]=blk[2]=blk[3]=blk[4]=blk[5]=blk[6]=blk[7]=blk[0]<<3;
      return 0;
	}

	x0 = (blk[0]<<11) + 128; /* for proper rounding in the fourth stage */

	/* first stage */
	x8 = W7*(x4+x5);
	x4 = x8 + (W1-W7)*x4;
	x5 = x8 - (W1+W7)*x5;
	x8 = W3*(x6+x7);
	x6 = x8 - (W3-W5)*x6;
	x7 = x8 - (W3+W5)*x7;

	/* second stage */
	x8 = x0 + x1;
	x0 -= x1;
	x1 = W6*(x3+x2);
	x2 = x1 - (W2+W6)*x2;
	x3 = x1 + (W2-W6)*x3;
	x1 = x4 + x6;
	x4 -= x6;
	x6 = x5 + x7;
	x5 -= x7;

	/* third stage */
	x7 = x8 + x3;
	x8 -= x3;
	x3 = x0 + x2;
	x0 -= x2;
	x2 = (181*(x4+x5)+128)>>8;
	x4 = (181*(x4-x5)+128)>>8;

	/* fourth stage */
	blk[0] = (x7+x1)>>8;
	blk[1] = (x3+x2)>>8;
	blk[2] = (x0+x4)>>8;
	blk[3] = (x8+x6)>>8;
	blk[4] = (x8-x6)>>8;
	blk[5] = (x0-x4)>>8;
	blk[6] = (x3-x2)>>8;
	blk[7] = (x7-x1)>>8;
	return 0;
}

/* column (vertical) IDCT
 *
 *             7                         pi         1
 * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l )
 *            l=0                        8          2
 *
 * where: c[0]    = 1/1024
 *        c[1..7] = (1/1024)*sqrt(2)
 */

int mpeg3video_idctcol(short *blk)
{
  int x0, x1, x2, x3, x4, x5, x6, x7, x8;

  /* shortcut */
  if (!((x1 = (blk[8 * 4]<<8)) | (x2 = blk[8 * 6]) | (x3 = blk[8 * 2]) |
        (x4 = blk[8*1]) | (x5 = blk[8 * 7]) | (x6 = blk[8 * 5]) | (x7 = blk[8 * 3]))){
    blk[8*0]=blk[8*1]=blk[8 * 2]=blk[8 * 3]=blk[8 * 4]=blk[8 * 5]=blk[8 * 6]=blk[8 * 7]=
      (blk[8*0]+32)>>6;
    return 0;
  }

	x0 = (blk[8*0]<<8) + 8192;

	/* first stage */
	x8 = W7*(x4+x5) + 4;
	x4 = (x8+(W1-W7)*x4)>>3;
	x5 = (x8-(W1+W7)*x5)>>3;
	x8 = W3*(x6+x7) + 4;
	x6 = (x8-(W3-W5)*x6)>>3;
	x7 = (x8-(W3+W5)*x7)>>3;

	/* second stage */
	x8 = x0 + x1;
	x0 -= x1;
	x1 = W6*(x3+x2) + 4;
	x2 = (x1-(W2+W6)*x2)>>3;
	x3 = (x1+(W2-W6)*x3)>>3;
	x1 = x4 + x6;
	x4 -= x6;
	x6 = x5 + x7;
	x5 -= x7;

	/* third stage */
	x7 = x8 + x3;
	x8 -= x3;
	x3 = x0 + x2;
	x0 -= x2;
	x2 = (181 * (x4 + x5) + 128) >> 8;
	x4 = (181 * (x4 - x5) + 128) >> 8;

	/* fourth stage */
	blk[8 * 0] = (x7 + x1) >> 14;
	blk[8 * 1] = (x3 + x2) >> 14;
	blk[8 * 2] = (x0 + x4) >> 14;
	blk[8 * 3] = (x8 + x6) >> 14;
	blk[8 * 4] = (x8 - x6) >> 14;
	blk[8 * 5] = (x0 - x4) >> 14;
	blk[8 * 6] = (x3 - x2) >> 14;
	blk[8 * 7] = (x7 - x1) >> 14;
	return 0;
}


/* two dimensional inverse discrete cosine transform */
void mpeg3video_idct_conversion(short* block)
{
	int i;
	for(i = 0; i < 8; i++) mpeg3video_idctrow(block + 8 * i);
	for(i = 0; i < 8; i++) mpeg3video_idctcol(block + i);
}