www.pudn.com > NETVIDEO.rar > idct.c

#include "idct.h" 
#include  
 
/**********************************************************/ 
/* 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); 
}