1 /* fdctref.c, forward discrete cosine transform, double precision */
3 /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
6 * Disclaimer of Warranty
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.
16 * This disclaimer of warranty extends to the user of these programs and user's
17 * customers, employees, agents, transferees, successors, and assigns.
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
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
36 # define PI 3.14159265358979323846
40 /* global declarations */
41 void init_fdct (void);
42 void fdct (short *block);
45 static double c[8][8]; /* transform coefficients */
54 s = (i==0) ? sqrt(0.125) : 0.5;
57 c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
68 for(i = 0; i < 8; i++)
69 for(j = 0; j < 8; j++)
74 * for(k = 0; k < 8; k++)
75 * s += c[j][k] * block[8 * i + k];
77 s += c[j][0] * block[8 * i + 0];
78 s += c[j][1] * block[8 * i + 1];
79 s += c[j][2] * block[8 * i + 2];
80 s += c[j][3] * block[8 * i + 3];
81 s += c[j][4] * block[8 * i + 4];
82 s += c[j][5] * block[8 * i + 5];
83 s += c[j][6] * block[8 * i + 6];
84 s += c[j][7] * block[8 * i + 7];
89 for(j = 0; j < 8; j++)
90 for(i = 0; i < 8; i++)
95 * for(k = 0; k < 8; k++)
96 * s += c[i][k] * tmp[8 * k + j];
98 s += c[i][0] * tmp[8 * 0 + j];
99 s += c[i][1] * tmp[8 * 1 + j];
100 s += c[i][2] * tmp[8 * 2 + j];
101 s += c[i][3] * tmp[8 * 3 + j];
102 s += c[i][4] * tmp[8 * 4 + j];
103 s += c[i][5] * tmp[8 * 5 + j];
104 s += c[i][6] * tmp[8 * 6 + j];
105 s += c[i][7] * tmp[8 * 7 + j];
108 block[8 * i + j] = (short)floor(s + 0.499999);
110 * reason for adding 0.499999 instead of 0.5:
111 * s is quite often x.5 (at least for i and/or j = 0 or 4)
112 * and setting the rounding threshold exactly to 0.5 leads to an
113 * extremely high arithmetic implementation dependency of the result;
114 * s being between x.5 and x.500001 (which is now incorrectly rounded
115 * downwards instead of upwards) is assumed to occur less often
121 /* perform IDCT matrix multiply for 8x8 coefficient block */
127 double partial_product;
133 partial_product = 0.0;
136 partial_product+= c[k][j]*block[8*i+k];
138 tmp[8*i+j] = partial_product;
141 /* Transpose operation is integrated into address mapping by switching
142 loop order of i and j */
147 partial_product = 0.0;
150 partial_product+= c[k][i]*tmp[8*k+j];
152 v = (int) floor(partial_product+0.5);