SVN=114204

1 files changed, 84 insertions, 0 deletions

diff --git a/src/lib/math/atan.go b/src/lib/math/atan.go
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+++ b/src/lib/math/atan.go
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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package atan
+
+export	atan
+
+/*
+	floating-point arctangent
+
+	atan returns the value of the arctangent of its
+	argument in the range [-pi/2,pi/2].
+	there are no error returns.
+	coefficients are #5077 from Hart & Cheney. (19.56D)
+*/
+
+
+const
+(
+	p4	= .161536412982230228262e2;
+	p3	= .26842548195503973794141e3;
+	p2	= .11530293515404850115428136e4;
+	p1	= .178040631643319697105464587e4;
+	p0	= .89678597403663861959987488e3;
+	q4	= .5895697050844462222791e2;
+	q3	= .536265374031215315104235e3;
+	q2	= .16667838148816337184521798e4;
+	q1	= .207933497444540981287275926e4;
+	q0	= .89678597403663861962481162e3;
+	pio2	= .15707963267948966192313216e1;
+	pio4	= .7853981633974483096156608e0;
+	sq2p1	= .2414213562373095048802e1;		// sqrt(2)+1
+	sq2m1	= .414213562373095048802e0;		// sqrt(2)-1
+)
+
+/*
+	xatan evaluates a series valid in the
+	range [-0.414...,+0.414...]. (tan(pi/8))
+ */
+
+func
+xatan(arg double) double
+{
+	var argsq, value double;
+
+	argsq = arg*arg;
+	value = ((((p4*argsq + p3)*argsq + p2)*argsq + p1)*argsq + p0);
+	value = value/(((((argsq + q4)*argsq + q3)*argsq + q2)*argsq + q1)*argsq + q0);
+	return value*arg;
+}
+
+/*
+	satan reduces its argument (known to be positive)
+	to the range [0,0.414...] and calls xatan.
+ */
+
+func
+satan(arg double) double
+{
+
+	if arg < sq2m1 {
+		return xatan(arg);
+	}
+	if arg > sq2p1 {
+		return pio2 - xatan(1/arg);
+	}
+	return pio4 + xatan((arg-1)/(arg+1));
+}
+
+/*
+	atan makes its argument positive and
+	calls the inner routine satan.
+ */
+
+func
+atan(arg double) double
+{
+
+	if arg > 0 {
+		return satan(arg);
+	}
+	return -satan(-arg);
+}