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comparison spandsp-0.0.6pre17/src/spandsp/arctan2.h @ 4:26cd8f1ef0b1
import spandsp-0.0.6pre17
author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
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date | Fri, 25 Jun 2010 15:50:58 +0200 |
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1 /* | |
2 * SpanDSP - a series of DSP components for telephony | |
3 * | |
4 * arctan2.h - A quick rough approximate arc tan | |
5 * | |
6 * Written by Steve Underwood <steveu@coppice.org> | |
7 * | |
8 * Copyright (C) 2003 Steve Underwood | |
9 * | |
10 * All rights reserved. | |
11 * | |
12 * This program is free software; you can redistribute it and/or modify | |
13 * it under the terms of the GNU Lesser General Public License version 2.1, | |
14 * as published by the Free Software Foundation. | |
15 * | |
16 * This program is distributed in the hope that it will be useful, | |
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
19 * GNU Lesser General Public License for more details. | |
20 * | |
21 * You should have received a copy of the GNU Lesser General Public | |
22 * License along with this program; if not, write to the Free Software | |
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
24 * | |
25 * $Id: arctan2.h,v 1.13 2008/05/29 13:04:19 steveu Exp $ | |
26 */ | |
27 | |
28 /*! \file */ | |
29 | |
30 #if !defined(_SPANDSP_ARCTAN2_H_) | |
31 #define _SPANDSP_ARCTAN2_H_ | |
32 | |
33 /*! \page arctan2_page Fast approximate four quadrant arc-tangent | |
34 \section arctan2_page_sec_1 What does it do? | |
35 This module provides a fast approximate 4-quadrant arc tangent function, | |
36 based on something at dspguru.com. The worst case error is about 4.07 degrees. | |
37 This is fine for many "where am I" type evaluations in comms. work. | |
38 | |
39 \section arctan2_page_sec_2 How does it work? | |
40 ???. | |
41 */ | |
42 | |
43 #if defined(__cplusplus) | |
44 extern "C" | |
45 { | |
46 #endif | |
47 | |
48 /* This returns its answer as a signed 32 bit integer phase value. */ | |
49 static __inline__ int32_t arctan2(float y, float x) | |
50 { | |
51 float abs_y; | |
52 float angle; | |
53 | |
54 if (x == 0.0f || y == 0.0f) | |
55 return 0; | |
56 | |
57 abs_y = fabsf(y); | |
58 | |
59 /* If we are in quadrant II or III, flip things around */ | |
60 if (x < 0.0f) | |
61 angle = 3.0f - (x + abs_y)/(abs_y - x); | |
62 else | |
63 angle = 1.0f - (x - abs_y)/(abs_y + x); | |
64 angle *= 536870912.0f; | |
65 | |
66 /* If we are in quadrant III or IV, negate to return an | |
67 answer in the range +-pi */ | |
68 if (y < 0.0f) | |
69 angle = -angle; | |
70 return (int32_t) angle; | |
71 } | |
72 /*- End of function --------------------------------------------------------*/ | |
73 | |
74 #if 0 | |
75 /* This returns its answer in radians, in the range +-pi. */ | |
76 static __inline__ float arctan2f(float y, float x) | |
77 { | |
78 float angle; | |
79 float fx; | |
80 float fy; | |
81 | |
82 if (x == 0.0f || y == 0.0f) | |
83 return 0; | |
84 fx = fabsf(x); | |
85 fy = fabsf(y); | |
86 /* Deal with the octants */ | |
87 /* N.B. 0.28125 == (1/4 + 1/32) */ | |
88 if (fy > fx) | |
89 angle = 3.1415926f/2.0f - fx*fy/(y*y + 0.28125f*x*x); | |
90 else | |
91 angle = fy*fx/(x*x + 0.28125f*y*y); | |
92 | |
93 /* Deal with the quadrants, to bring the final answer to the range +-pi */ | |
94 if (x < 0.0f) | |
95 angle = 3.1415926f - angle; | |
96 if (y < 0.0f) | |
97 angle = -angle; | |
98 return angle; | |
99 } | |
100 /*- End of function --------------------------------------------------------*/ | |
101 #endif | |
102 | |
103 #if defined(__cplusplus) | |
104 } | |
105 #endif | |
106 | |
107 #endif | |
108 /*- End of file ------------------------------------------------------------*/ |