fbui | Framebuffer-based graphical environment |
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libfbui/MPEG/idctref.c
1 /* Reference_IDCT.c, Inverse Discrete Fourier 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 /* Perform IEEE 1180 reference (64-bit floating point, separable 8x1
31 * direct matrix multiply) Inverse Discrete Cosine Transform
32 */
33
34
35 /* Here we use math.h to generate constants. Compiler results may
36 vary a little */
37
38 #include <math.h>
39
40 #include "config.h"
41
42 #ifndef PI
43 # ifdef M_PI
44 # define PI M_PI
45 # else
46 # define PI 3.14159265358979323846
47 # endif
48 #endif
49
50 /* global declarations */
51 void Initialize_Fast_IDCTref _ANSI_ARGS_((void));
52 void Reference_IDCT _ANSI_ARGS_((short *block));
53
54 /* private data */
55
56 /* cosine transform matrix for 8x1 IDCT */
57 static double c[8][8];
58
59 /* initialize DCT coefficient matrix */
60
61 void Initialize_Reference_IDCT()
62 {
63 int freq, time;
64 double scale;
65
66 for (freq=0; freq < 8; freq++)
67 {
68 scale = (freq == 0) ? sqrt(0.125) : 0.5;
69 for (time=0; time<8; time++)
70 c[freq][time] = scale*cos((PI/8.0)*freq*(time + 0.5));
71 }
72 }
73
74 /* perform IDCT matrix multiply for 8x8 coefficient block */
75
76 void Reference_IDCT(block)
77 short *block;
78 {
79 int i, j, k, v;
80 double partial_product;
81 double tmp[64];
82
83 for (i=0; i<8; i++)
84 for (j=0; j<8; j++)
85 {
86 partial_product = 0.0;
87
88 for (k=0; k<8; k++)
89 partial_product+= c[k][j]*block[8*i+k];
90
91 tmp[8*i+j] = partial_product;
92 }
93
94 /* Transpose operation is integrated into address mapping by switching
95 loop order of i and j */
96
97 for (j=0; j<8; j++)
98 for (i=0; i<8; i++)
99 {
100 partial_product = 0.0;
101
102 for (k=0; k<8; k++)
103 partial_product+= c[k][i]*tmp[8*k+j];
104
105 v = (int) floor(partial_product+0.5);
106 block[8*i+j] = (v<-256) ? -256 : ((v>255) ? 255 : v);
107 }
108 }
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