/* Reference_IDCT.c, 離散傅利葉反變換*/#include <math.h>#include "config.h"#ifndef PI# ifdef M_PI#  define PI M_PI# else#  define PI 3.14159265358979323846# endif#endif/* global declarations */void Initialize_Fast_IDCTref _ANSI_ARGS_((void));void Reference_IDCT _ANSI_ARGS_((short *block));/* private data *//* cosine transform matrix for 8x1 IDCT */static double c[8][8];/* initialize DCT coefficient matrix */void Initialize_Reference_IDCT(){  int freq, time;  double scale;  for (freq=0; freq < 8; freq++)  {    scale = (freq == 0) ? sqrt(0.125) : 0.5;    for (time=0; time<8; time++)      c[freq][time] = scale*cos((PI/8.0)*freq*(time + 0.5));  }}/* perform IDCT matrix multiply for 8x8 coefficient block */void Reference_IDCT(block)short *block;{  int i, j, k, v;  double partial_product;  double tmp[64];  for (i=0; i<8; i++)    for (j=0; j<8; j++)    {      partial_product = 0.0;      for (k=0; k<8; k++)        partial_product+= c[k][j]*block[8*i+k];      tmp[8*i+j] = partial_product;    }  /* Transpose operation is integrated into address mapping by switching      loop order of i and j */  for (j=0; j<8; j++)    for (i=0; i<8; i++)    {      partial_product = 0.0;      for (k=0; k<8; k++)        partial_product+= c[k][i]*tmp[8*k+j];      v = (int) floor(partial_product+0.5);      block[8*i+j] = (v<-256) ? -256 : ((v>255) ? 255 : v);    }}