--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.6pre17/src/spandsp/arctan2.h	Fri Jun 25 15:50:58 2010 +0200
@@ -0,0 +1,108 @@
+/*
+ * 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 Lesser General Public License version 2.1,
+ * 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser 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 1.13 2008/05/29 13:04:19 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 == 0.0f  ||  y == 0.0f)
+        return 0;
+    
+    abs_y = fabsf(y);
+
+    /* If we are in quadrant II or III, flip things around */
+    if (x < 0.0f)
+        angle = 3.0f - (x + abs_y)/(abs_y - x);
+    else
+        angle = 1.0f - (x - abs_y)/(abs_y + x);
+    angle *= 536870912.0f;
+
+    /* If we are in quadrant III or IV, negate to return an
+       answer in the range +-pi */
+    if (y < 0.0f)
+        angle = -angle;
+    return (int32_t) angle;
+}
+/*- End of function --------------------------------------------------------*/
+
+#if 0
+/* This returns its answer in radians, in the range +-pi. */
+static __inline__ float arctan2f(float y, float x)
+{
+    float angle;
+    float fx;
+    float fy;
+
+    if (x == 0.0f  ||  y == 0.0f)
+        return 0;
+    fx = fabsf(x);
+    fy = fabsf(y);
+    /* Deal with the octants */
+    /* N.B. 0.28125 == (1/4 + 1/32) */
+    if (fy > fx)
+        angle = 3.1415926f/2.0f - fx*fy/(y*y + 0.28125f*x*x);
+    else
+        angle = fy*fx/(x*x + 0.28125f*y*y);
+    
+    /* Deal with the quadrants, to bring the final answer to the range +-pi */
+    if (x < 0.0f)
+        angle = 3.1415926f - angle;
+    if (y < 0.0f)
+        angle = -angle;
+    return angle;
+}
+/*- End of function --------------------------------------------------------*/
+#endif
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/