spandsp 0.0.6
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00001 /* 00002 * SpanDSP - a series of DSP components for telephony 00003 * 00004 * arctan2.h - A quick rough approximate arc tan 00005 * 00006 * Written by Steve Underwood <steveu@coppice.org> 00007 * 00008 * Copyright (C) 2003 Steve Underwood 00009 * 00010 * All rights reserved. 00011 * 00012 * This program is free software; you can redistribute it and/or modify 00013 * it under the terms of the GNU Lesser General Public License version 2.1, 00014 * as published by the Free Software Foundation. 00015 * 00016 * This program is distributed in the hope that it will be useful, 00017 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00018 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 00019 * GNU Lesser General Public License for more details. 00020 * 00021 * You should have received a copy of the GNU Lesser General Public 00022 * License along with this program; if not, write to the Free Software 00023 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 00024 */ 00025 00026 /*! \file */ 00027 00028 #if !defined(_SPANDSP_ARCTAN2_H_) 00029 #define _SPANDSP_ARCTAN2_H_ 00030 00031 /*! \page arctan2_page Fast approximate four quadrant arc-tangent 00032 \section arctan2_page_sec_1 What does it do? 00033 This module provides a fast approximate 4-quadrant arc tangent function, 00034 based on something at dspguru.com. The worst case error is about 4.07 degrees. 00035 This is fine for many "where am I" type evaluations in comms. work. 00036 00037 \section arctan2_page_sec_2 How does it work? 00038 ???. 00039 */ 00040 00041 #if defined(__cplusplus) 00042 extern "C" 00043 { 00044 #endif 00045 00046 /* This returns its answer as a signed 32 bit integer phase value. */ 00047 static __inline__ int32_t arctan2(float y, float x) 00048 { 00049 float abs_y; 00050 float angle; 00051 00052 if (x == 0.0f || y == 0.0f) 00053 return 0; 00054 00055 abs_y = fabsf(y); 00056 00057 /* If we are in quadrant II or III, flip things around */ 00058 if (x < 0.0f) 00059 angle = 3.0f - (x + abs_y)/(abs_y - x); 00060 else 00061 angle = 1.0f - (x - abs_y)/(abs_y + x); 00062 angle *= 536870912.0f; 00063 00064 /* If we are in quadrant III or IV, negate to return an 00065 answer in the range +-pi */ 00066 if (y < 0.0f) 00067 angle = -angle; 00068 return (int32_t) angle; 00069 } 00070 /*- End of function --------------------------------------------------------*/ 00071 00072 #if 0 00073 /* This returns its answer in radians, in the range +-pi. */ 00074 static __inline__ float arctan2f(float y, float x) 00075 { 00076 float angle; 00077 float fx; 00078 float fy; 00079 00080 if (x == 0.0f || y == 0.0f) 00081 return 0; 00082 fx = fabsf(x); 00083 fy = fabsf(y); 00084 /* Deal with the octants */ 00085 /* N.B. 0.28125 == (1/4 + 1/32) */ 00086 if (fy > fx) 00087 angle = 3.1415926f/2.0f - fx*fy/(y*y + 0.28125f*x*x); 00088 else 00089 angle = fy*fx/(x*x + 0.28125f*y*y); 00090 00091 /* Deal with the quadrants, to bring the final answer to the range +-pi */ 00092 if (x < 0.0f) 00093 angle = 3.1415926f - angle; 00094 if (y < 0.0f) 00095 angle = -angle; 00096 return angle; 00097 } 00098 /*- End of function --------------------------------------------------------*/ 00099 #endif 00100 00101 #if defined(__cplusplus) 00102 } 00103 #endif 00104 00105 #endif 00106 /*- End of file ------------------------------------------------------------*/