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fixp-arith.h
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1 #ifndef _FIXP_ARITH_H
2 #define _FIXP_ARITH_H
3 
4 /*
5  * Simplistic fixed-point arithmetics.
6  * Hmm, I'm probably duplicating some code :(
7  *
8  * Copyright (c) 2002 Johann Deneux
9  */
10 
11 /*
12  * This program is free software; you can redistribute it and/or modify
13  * it under the terms of the GNU General Public License as published by
14  * the Free Software Foundation; either version 2 of the License, or
15  * (at your option) any later version.
16  *
17  * This program is distributed in the hope that it will be useful,
18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20  * GNU General Public License for more details.
21  *
22  * You should have received a copy of the GNU General Public License
23  * along with this program; if not, write to the Free Software
24  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25  *
26  * Should you need to contact me, the author, you can do so by
27  * e-mail - mail your message to <[email protected]>
28  */
29 
30 #include <linux/types.h>
31 
32 /* The type representing fixed-point values */
33 typedef s16 fixp_t;
34 
35 #define FRAC_N 8
36 #define FRAC_MASK ((1<<FRAC_N)-1)
37 
38 /* Not to be used directly. Use fixp_{cos,sin} */
39 static const fixp_t cos_table[46] = {
40  0x0100, 0x00FF, 0x00FF, 0x00FE, 0x00FD, 0x00FC, 0x00FA, 0x00F8,
41  0x00F6, 0x00F3, 0x00F0, 0x00ED, 0x00E9, 0x00E6, 0x00E2, 0x00DD,
42  0x00D9, 0x00D4, 0x00CF, 0x00C9, 0x00C4, 0x00BE, 0x00B8, 0x00B1,
43  0x00AB, 0x00A4, 0x009D, 0x0096, 0x008F, 0x0087, 0x0080, 0x0078,
44  0x0070, 0x0068, 0x005F, 0x0057, 0x004F, 0x0046, 0x003D, 0x0035,
45  0x002C, 0x0023, 0x001A, 0x0011, 0x0008, 0x0000
46 };
47 
48 
49 /* a: 123 -> 123.0 */
50 static inline fixp_t fixp_new(s16 a)
51 {
52  return a<<FRAC_N;
53 }
54 
55 /* a: 0xFFFF -> -1.0
56  0x8000 -> 1.0
57  0x0000 -> 0.0
58 */
59 static inline fixp_t fixp_new16(s16 a)
60 {
61  return ((s32)a)>>(16-FRAC_N);
62 }
63 
64 static inline fixp_t fixp_cos(unsigned int degrees)
65 {
66  int quadrant = (degrees / 90) & 3;
67  unsigned int i = degrees % 90;
68 
69  if (quadrant == 1 || quadrant == 3)
70  i = 90 - i;
71 
72  i >>= 1;
73 
74  return (quadrant == 1 || quadrant == 2)? -cos_table[i] : cos_table[i];
75 }
76 
77 static inline fixp_t fixp_sin(unsigned int degrees)
78 {
79  return -fixp_cos(degrees + 90);
80 }
81 
82 static inline fixp_t fixp_mult(fixp_t a, fixp_t b)
83 {
84  return ((s32)(a*b))>>FRAC_N;
85 }
86 
87 #endif