hvirtual/mpeg2enc/fdctref.c

   1 /* fdctref.c, forward discrete cosine transform, double precision           */
   2
   3 /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
   4
   5 /*
   6  * Disclaimer of Warranty
   7  *
   8  * These software programs are available to the user without any license fee or
   9  * royalty on an "as is" basis.  The MPEG Software Simulation Group disclaims
  10  * any and all warranties, whether express, implied, or statuary, including any
  11  * implied warranties or merchantability or of fitness for a particular
  12  * purpose.  In no event shall the copyright-holder be liable for any
  13  * incidental, punitive, or consequential damages of any kind whatsoever
  14  * arising from the use of these programs.
  15  *
  16  * This disclaimer of warranty extends to the user of these programs and user's
  17  * customers, employees, agents, transferees, successors, and assigns.
  18  *
  19  * The MPEG Software Simulation Group does not represent or warrant that the
  20  * programs furnished hereunder are free of infringement of any third-party
  21  * patents.
  22  *
  23  * Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
  24  * are subject to royalty fees to patent holders.  Many of these patents are
  25  * general enough such that they are unavoidable regardless of implementation
  26  * design.
  27  *
  28  */
  29
  30 #include <math.h>
  31
  32 #include "config.h"
  33
  34 #ifndef PI
  35 # ifdef M_PI
  36 #  define PI M_PI
  37 # else
  38 #  define PI 3.14159265358979323846
  39 # endif
  40 #endif
  41
  42 /* global declarations */
  43 void init_fdct _ANSI_ARGS_((void));
  44 void fdct _ANSI_ARGS_((short *block));
  45
  46 /* private data */
  47 static double c[8][8]; /* transform coefficients */
  48
  49 void init_fdct()
  50 {
  51   int i, j;
  52   double s;
  53
  54   for (i=0; i<8; i++)
  55   {
  56     s = (i==0) ? sqrt(0.125) : 0.5;
  57
  58     for (j=0; j<8; j++)
  59       c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
  60   }
  61 }
  62
  63 void fdct(block)
  64 short *block;
  65 {
  66         register int i, j;
  67         double s;
  68         double tmp[64];
  69
  70         for(i = 0; i < 8; i++)
  71         for(j = 0; j < 8; j++)
  72         {
  73                 s = 0.0;
  74
  75 /*
  76  *              for(k = 0; k < 8; k++)
  77  *                      s += c[j][k] * block[8 * i + k];
  78  */
  79                 s += c[j][0] * block[8 * i + 0];
  80                 s += c[j][1] * block[8 * i + 1];
  81                 s += c[j][2] * block[8 * i + 2];
  82                 s += c[j][3] * block[8 * i + 3];
  83                 s += c[j][4] * block[8 * i + 4];
  84                 s += c[j][5] * block[8 * i + 5];
  85                 s += c[j][6] * block[8 * i + 6];
  86                 s += c[j][7] * block[8 * i + 7];
  87
  88                 tmp[8 * i + j] = s;
  89         }
  90
  91         for(j = 0; j < 8; j++)
  92         for(i = 0; i < 8; i++)
  93         {
  94                 s = 0.0;
  95
  96 /*
  97  *              for(k = 0; k < 8; k++)
  98  *                  s += c[i][k] * tmp[8 * k + j];
  99  */
 100                 s += c[i][0] * tmp[8 * 0 + j];
 101                 s += c[i][1] * tmp[8 * 1 + j];
 102                 s += c[i][2] * tmp[8 * 2 + j];
 103                 s += c[i][3] * tmp[8 * 3 + j];
 104                 s += c[i][4] * tmp[8 * 4 + j];
 105                 s += c[i][5] * tmp[8 * 5 + j];
 106                 s += c[i][6] * tmp[8 * 6 + j];
 107                 s += c[i][7] * tmp[8 * 7 + j];
 108
 109                 block[8 * i + j] = (int)floor(s + 0.499999);
 110 /*
 111  * reason for adding 0.499999 instead of 0.5:
 112  * s is quite often x.5 (at least for i and/or j = 0 or 4)
 113  * and setting the rounding threshold exactly to 0.5 leads to an
 114  * extremely high arithmetic implementation dependency of the result;
 115  * s being between x.5 and x.500001 (which is now incorrectly rounded
 116  * downwards instead of upwards) is assumed to occur less often
 117  * (if at all)
 118  */
 119       }
 120 }