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+/* -*- c++ -*- */
+/*
+ * Copyright 2003,2005 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+/*
+ * mathematical odds and ends.
+ */
+
+#ifndef _GR_MATH_H_
+#define _GR_MATH_H_
+
+long gr_gcd (long m, long n);
+
+// returns a non-zero value if value is "not-a-number" (NaN), and 0 otherwise
+int gr_isnan (double value);
+
+// returns a non-zero value if the value of x has its sign bit set.
+//
+// This  is  not  the  same  as `x < 0.0', because IEEE 754 floating point
+// allows zero to be signed.  The comparison `-0.0 < 0.0'  is  false,  but
+// `gr_signbit (-0.0)' will return a nonzero value.
+
+int gr_signbit (double x);
+  
+/*!
+ * \brief Fast arc tangent using table lookup and linear interpolation
+ *
+ * \param y component of input vector
+ * \param x component of input vector
+ * \returns float angle angle of vector (x, y) in radians
+ *
+ * This function calculates the angle of the vector (x,y) based on a
+ * table lookup and linear interpolation. The table uses a 256 point
+ * table covering -45 to +45 degrees and uses symetry to determine the
+ * final angle value in the range of -180 to 180 degrees. Note that
+ * this function uses the small angle approximation for values close
+ * to zero. This routine calculates the arc tangent with an average
+ * error of +/- 0.045 degrees.
+ */
+float gr_fast_atan2f(float y, float x);
+
+#endif /* _GR_MATH_H_ */