67 lines
1.2 KiB
C++
67 lines
1.2 KiB
C++
#include "idctref.h"
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#include <math.h>
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#ifndef PI
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# ifdef M_PI
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# define PI M_PI
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# else
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# define PI 3.14159265358979323846
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# endif
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#endif
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bool IDCTRef::initted = false;
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double IDCTRef::c[8][8]; /* cosine transform matrix for 8x1 IDCT */
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/* initialize DCT coefficient matrix */
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void IDCTRef::init()
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{
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if (!initted)
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{
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int freq, time;
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for (freq=0; freq < 8; freq++)
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{
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double scale = (freq == 0) ? sqrt(0.125) : 0.5;
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for (time=0; time<8; time++)
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c[freq][time] = scale*cos((PI/8.0)*freq*(time + 0.5));
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}
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initted=true;
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}
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}
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/* perform IDCT matrix multiply for 8x8 coefficient block */
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void IDCTRef::idct(short *block)
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{
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int i, j, k, v;
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double partial_product;
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double tmp[64];
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for (i=0; i<8; i++)
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for (j=0; j<8; j++)
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{
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partial_product = 0.0;
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for (k=0; k<8; k++)
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partial_product+= c[k][j]*block[8*i+k];
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tmp[8*i+j] = partial_product;
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}
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/* Transpose operation is integrated into address mapping by switching
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loop order of i and j */
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for (j=0; j<8; j++)
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for (i=0; i<8; i++)
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{
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partial_product = 0.0;
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for (k=0; k<8; k++)
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partial_product+= c[k][i]*tmp[8*k+j];
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v = (int)floor(partial_product+0.5);
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block[8*i+j] = (v<-256) ? -256 : ((v>255) ? 255 : v);
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}
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}
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