/* * SpanDSP - a series of DSP components for telephony * * arctan2.h - A quick rough approximate arc tan * * Written by Steve Underwood <steveu@coppice.org> * * Copyright (C) 2003 Steve Underwood * * All rights reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2, as * published by the Free Software Foundation. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * * $Id: arctan2.h,v 1.10 2007/04/08 08:16:17 steveu Exp $ *//*! \file */#if !defined(_SPANDSP_ARCTAN2_H_)#define _SPANDSP_ARCTAN2_H_/*! \page arctan2_page Fast approximate four quadrant arc-tangent\section arctan2_page_sec_1 What does it do?This module provides a fast approximate 4-quadrant arc tangent function,based on something at dspguru.com. The worst case error is about 4.07 degrees.This is fine for many "where am I" type evaluations in comms. work.\section arctan2_page_sec_2 How does it work????.*/#if defined(__cplusplus)extern "C"{#endif/* This returns its answer as a signed 32 bit integer phase value. */static __inline__ int32_t arctan2(float y, float x){    float abs_y;    float angle;    if (x == 0.0  ||  y == 0.0)        return 0;        abs_y = fabsf(y);    /* If we are in quadrant II or III, flip things around */    if (x < 0.0)        angle = 3.0f - (x + abs_y)/(abs_y - x);    else        angle = 1.0f - (x - abs_y)/(abs_y + x);    angle *= 536870912.0;    /* If we are in quadrant III or IV, negate to return an       answer in the range +-pi */    if (y < 0.0)        angle = -angle;    return (int32_t) angle;}/*- End of function --------------------------------------------------------*/#if defined(__cplusplus)}#endif#endif/*- End of file ------------------------------------------------------------*/