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5
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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * arctan2.h - A quick rough approximate arc tan
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2003 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * $Id: arctan2.h,v 1.7 2006/10/24 13:22:01 steveu Exp $
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26 */
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27
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28 /*! \file */
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29
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30 #if !defined(_ARCTAN2_H_)
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31 #define _ARCTAN2_H_
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32
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33 /*! \page arctan2_page Fast approximate four quadrant arc-tangent
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34 \section arctan2_page_sec_1 What does it do?
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35 This module provides a fast approximate 4-quadrant arc tangent function,
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36 based on something at dspguru.com. The worst case error is about 4.07 degrees.
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37 This is fine for many "where am I" type evaluations in comms. work.
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38
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39 \section arctan2_page_sec_2 How does it work?
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40 ???.
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41 */
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42
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43 #ifdef __cplusplus
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44 extern "C" {
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45 #endif
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46
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47 /* This returns its answer as a signed 32 bit integer phase value. */
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48 static __inline__ int32_t arctan2(float y, float x)
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49 {
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50 float abs_y;
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51 float angle;
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52
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53 if (x == 0.0 || y == 0.0)
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54 return 0;
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55
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56 abs_y = fabsf(y);
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57
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58 /* If we are in quadrant II or III, flip things around */
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59 if (x < 0.0)
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60 angle = 3.0f - (x + abs_y)/(abs_y - x);
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61 else
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62 angle = 1.0f - (x - abs_y)/(abs_y + x);
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63 angle *= 536870912.0;
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64
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65 /* If we are in quadrant III or IV, negate to return an
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66 answer in the range +-pi */
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67 if (y < 0.0)
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68 angle = -angle;
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69 return (int32_t) angle;
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70 }
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71 /*- End of function --------------------------------------------------------*/
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72
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73 #ifdef __cplusplus
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74 }
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75 #endif
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76
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77 #endif
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78 /*- End of file ------------------------------------------------------------*/
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