3 * forward discrete cosine transform, double precision.
6 /* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
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39 # define PI 3.14159265358979323846
43 /* global declarations */
44 void init_fdct (void);
45 void fdct (short *block);
48 static double c[8][8]; /* transform coefficients */
57 s = (i==0) ? sqrt(0.125) : 0.5;
60 c[i][j] = s * cos((PI/8.0)*i*(j+0.5));
71 for(i = 0; i < 8; i++)
72 for(j = 0; j < 8; j++)
77 * for(k = 0; k < 8; k++)
78 * s += c[j][k] * block[8 * i + k];
80 s += c[j][0] * block[8 * i + 0];
81 s += c[j][1] * block[8 * i + 1];
82 s += c[j][2] * block[8 * i + 2];
83 s += c[j][3] * block[8 * i + 3];
84 s += c[j][4] * block[8 * i + 4];
85 s += c[j][5] * block[8 * i + 5];
86 s += c[j][6] * block[8 * i + 6];
87 s += c[j][7] * block[8 * i + 7];
92 for(j = 0; j < 8; j++)
93 for(i = 0; i < 8; i++)
98 * for(k = 0; k < 8; k++)
99 * s += c[i][k] * tmp[8 * k + j];
101 s += c[i][0] * tmp[8 * 0 + j];
102 s += c[i][1] * tmp[8 * 1 + j];
103 s += c[i][2] * tmp[8 * 2 + j];
104 s += c[i][3] * tmp[8 * 3 + j];
105 s += c[i][4] * tmp[8 * 4 + j];
106 s += c[i][5] * tmp[8 * 5 + j];
107 s += c[i][6] * tmp[8 * 6 + j];
108 s += c[i][7] * tmp[8 * 7 + j];
111 block[8 * i + j] = (short)floor(s + 0.499999);
113 * reason for adding 0.499999 instead of 0.5:
114 * s is quite often x.5 (at least for i and/or j = 0 or 4)
115 * and setting the rounding threshold exactly to 0.5 leads to an
116 * extremely high arithmetic implementation dependency of the result;
117 * s being between x.5 and x.500001 (which is now incorrectly rounded
118 * downwards instead of upwards) is assumed to occur less often
124 /* perform IDCT matrix multiply for 8x8 coefficient block */
130 double partial_product;
136 partial_product = 0.0;
139 partial_product+= c[k][j]*block[8*i+k];
141 tmp[8*i+j] = partial_product;
144 /* Transpose operation is integrated into address mapping by switching
145 loop order of i and j */
150 partial_product = 0.0;
153 partial_product+= c[k][i]*tmp[8*k+j];
155 v = (int) floor(partial_product+0.5);