jedioutcast/utils/roq2/mpeg/idctref.c

/* Reference_IDCT.c, Inverse Discrete Fourier 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.

 *

 */



/*  Perform IEEE 1180 reference (64-bit floating point, separable 8x1

 *  direct matrix multiply) Inverse Discrete Cosine Transform

*/





/* Here we use math.h to generate constants.  Compiler results may

   vary a little */



#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);

    }

}