/* idct.c, 反向快速離散余弦變換*//* 該代碼是在二進(jìn)制運(yùn)算下進(jìn)行的*//* 如右移 : (-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) *//* 函數(shù)聲明 */void init_idct(void);void idct(short *block);/*私有數(shù)據(jù) */static short iclip[1024]; static short *iclp;static void idctrow(short *blk);static void idctcol(short *blk);/* 行IDCT * *           7                       pi         1 * dst[k] = sum c[l] * src[l] * cos( -- * ( k + - ) * l ) *          l=0                      8          2 * * 其中: c[0]    = 128 *        c[1..7] = 128*sqrt(2) */static void idctrow(blk)short *blk;{  int x0, x1, x2, x3, x4, x5, x6, x7, x8;  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;  }  x0 = (blk[0]<<11) + 128;   /* 第一步 */  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;    /* 第二步*/  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;    /* 第三步 */  x7 = x8 + x3;  x8 -= x3;  x3 = x0 + x2;  x0 -= x2;  x2 = (181*(x4+x5)+128)>>8;  x4 = (181*(x4-x5)+128)>>8;    /* 第四步 */  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;}/* 列IDCT * *             7                         pi         1 * dst[8*k] = sum c[l] * src[8*l] * cos( -- * ( k + - ) * l ) *            l=0                        8          2 * * 其中: c[0]    = 1/1024 *        c[1..7] = (1/1024)*sqrt(2) */static void idctcol(blk)short *blk;{  int x0, x1, x2, x3, x4, x5, x6, x7, x8;  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]=      iclp[(blk[8*0]+32)>>6];    return;  }  x0 = (blk[8*0]<<8) + 8192;  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;    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;    x7 = x8 + x3;  x8 -= x3;  x3 = x0 + x2;  x0 -= x2;  x2 = (181*(x4+x5)+128)>>8;  x4 = (181*(x4-x5)+128)>>8;    blk[8*0] = iclp[(x7+x1)>>14];  blk[8*1] = iclp[(x3+x2)>>14];  blk[8*2] = iclp[(x0+x4)>>14];  blk[8*3] = iclp[(x8+x6)>>14];  blk[8*4] = iclp[(x8-x6)>>14];  blk[8*5] = iclp[(x0-x4)>>14];  blk[8*6] = iclp[(x3-x2)>>14];  blk[8*7] = iclp[(x7-x1)>>14];}/* 二維反向離散余弦變換*/void idct(block)short *block;{  int i;  for (i=0; i<8; i++)    idctrow(block+8*i);  for (i=0; i<8; i++)    idctcol(block+i);}void init_idct(){  int i;  iclp = iclip+512;  for (i= -512; i<512; i++)    iclp[i] = (i<-256) ? -256 : ((i>255) ? 255 : i);}