Mercurial > hg > audiostuff
comparison spandsp-0.0.3/spandsp-0.0.3/src/spandsp/arctan2.h @ 5:f762bf195c4b
import spandsp-0.0.3
| author | Peter Meerwald <pmeerw@cosy.sbg.ac.at> |
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| date | Fri, 25 Jun 2010 16:00:21 +0200 |
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| 4:26cd8f1ef0b1 | 5:f762bf195c4b |
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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 General Public License version 2, as | |
| 14 * 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 General Public License for more details. | |
| 20 * | |
| 21 * You should have received a copy of the GNU General Public License | |
| 22 * 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 1.7 2006/10/24 13:22:01 steveu Exp $ | |
| 26 */ | |
| 27 | |
| 28 /*! \file */ | |
| 29 | |
| 30 #if !defined(_ARCTAN2_H_) | |
| 31 #define _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 #ifdef __cplusplus | |
| 44 extern "C" { | |
| 45 #endif | |
| 46 | |
| 47 /* This returns its answer as a signed 32 bit integer phase value. */ | |
| 48 static __inline__ int32_t arctan2(float y, float x) | |
| 49 { | |
| 50 float abs_y; | |
| 51 float angle; | |
| 52 | |
| 53 if (x == 0.0 || y == 0.0) | |
| 54 return 0; | |
| 55 | |
| 56 abs_y = fabsf(y); | |
| 57 | |
| 58 /* If we are in quadrant II or III, flip things around */ | |
| 59 if (x < 0.0) | |
| 60 angle = 3.0f - (x + abs_y)/(abs_y - x); | |
| 61 else | |
| 62 angle = 1.0f - (x - abs_y)/(abs_y + x); | |
| 63 angle *= 536870912.0; | |
| 64 | |
| 65 /* If we are in quadrant III or IV, negate to return an | |
| 66 answer in the range +-pi */ | |
| 67 if (y < 0.0) | |
| 68 angle = -angle; | |
| 69 return (int32_t) angle; | |
| 70 } | |
| 71 /*- End of function --------------------------------------------------------*/ | |
| 72 | |
| 73 #ifdef __cplusplus | |
| 74 } | |
| 75 #endif | |
| 76 | |
| 77 #endif | |
| 78 /*- End of file ------------------------------------------------------------*/ |