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/* fdctref.c, forward discrete cosine transform, double precision */
/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
/*
* Disclaimer of Warranty
*
* These software programs are available to the user without any license fee or
* royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
* any and all warranties, whether express, implied, or statuary, including any
* implied warranties or merchantability or of fitness for a particular
* purpose. In no event shall the copyright-holder be liable for any
* incidental, punitive, or consequential damages of any kind whatsoever
* arising from the use of these programs.
*
* This disclaimer of warranty extends to the user of these programs and user's
* customers, employees, agents, transferees, successors, and assigns.
*
* The MPEG Software Simulation Group does not represent or warrant that the
* programs furnished hereunder are free of infringement of any third-party
* patents.
*
* Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
* are subject to royalty fees to patent holders. Many of these patents are
* general enough such that they are unavoidable regardless of implementation
* design.
*
*/
#include <math.h>
#ifndef PI
# ifdef M_PI
# define PI M_PI
# else
# define PI 3.14159265358979323846
# endif
#endif
/* global declarations */
void init_fdct (void);
void fdct (short *block);
/* private data */
static double c[8][8]; /* transform coefficients */
void init_fdct()
{
int i, j;
double s;
for (i=0; i<8; i++)
{
s = (i==0) ? sqrt(0.125) : 0.5;
for (j=0; j<8; j++)
c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
}
}
void fdct(block)
short *block;
{
register int i, j;
double s;
double tmp[64];
for(i = 0; i < 8; i++)
for(j = 0; j < 8; j++)
{
s = 0.0;
/*
* for(k = 0; k < 8; k++)
* s += c[j][k] * block[8 * i + k];
*/
s += c[j][0] * block[8 * i + 0];
s += c[j][1] * block[8 * i + 1];
s += c[j][2] * block[8 * i + 2];
s += c[j][3] * block[8 * i + 3];
s += c[j][4] * block[8 * i + 4];
s += c[j][5] * block[8 * i + 5];
s += c[j][6] * block[8 * i + 6];
s += c[j][7] * block[8 * i + 7];
tmp[8 * i + j] = s;
}
for(j = 0; j < 8; j++)
for(i = 0; i < 8; i++)
{
s = 0.0;
/*
* for(k = 0; k < 8; k++)
* s += c[i][k] * tmp[8 * k + j];
*/
s += c[i][0] * tmp[8 * 0 + j];
s += c[i][1] * tmp[8 * 1 + j];
s += c[i][2] * tmp[8 * 2 + j];
s += c[i][3] * tmp[8 * 3 + j];
s += c[i][4] * tmp[8 * 4 + j];
s += c[i][5] * tmp[8 * 5 + j];
s += c[i][6] * tmp[8 * 6 + j];
s += c[i][7] * tmp[8 * 7 + j];
block[8 * i + j] = (short)floor(s + 0.499999);
/*
* reason for adding 0.499999 instead of 0.5:
* s is quite often x.5 (at least for i and/or j = 0 or 4)
* and setting the rounding threshold exactly to 0.5 leads to an
* extremely high arithmetic implementation dependency of the result;
* s being between x.5 and x.500001 (which is now incorrectly rounded
* downwards instead of upwards) is assumed to occur less often
* (if at all)
*/
}
}
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