1 files changed, 67 insertions, 0 deletions
diff --git a/src/pkg/math/atan.go b/src/pkg/math/atan.go
new file mode 100644
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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 math
+
+import "math"
+
+/*
+ *	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)
+ */
+
+/*
+ *	xatan evaluates a series valid in the
+ *	range [-0.414...,+0.414...]. (tan(pi/8))
+ */
+func xatan(arg float64) float64 {
+	const
+	(
+		P4	= .161536412982230228262e2;
+		P3	= .26842548195503973794141e3;
+		P2	= .11530293515404850115428136e4;
+		P1	= .178040631643319697105464587e4;
+		P0	= .89678597403663861959987488e3;
+		Q4	= .5895697050844462222791e2;
+		Q3	= .536265374031215315104235e3;
+		Q2	= .16667838148816337184521798e4;
+		Q1	= .207933497444540981287275926e4;
+		Q0	= .89678597403663861962481162e3;
+	)
+	sq := arg*arg;
+	value := ((((P4*sq + P3)*sq + P2)*sq + P1)*sq + P0);
+	value = value/(((((sq + Q4)*sq + Q3)*sq + Q2)*sq + Q1)*sq + Q0);
+	return value*arg;
+}
+
+/*
+ *	satan reduces its argument (known to be positive)
+ *	to the range [0,0.414...] and calls xatan.
+ */
+func satan(arg float64) float64 {
+	if arg < Sqrt2 - 1 {
+		return xatan(arg);
+	}
+	if arg > Sqrt2 + 1 {
+		return Pi/2 - xatan(1/arg);
+	}
+	return Pi/4 + xatan((arg-1)/(arg+1));
+}
+
+/*
+ *	atan makes its argument positive and
+ *	calls the inner routine satan.
+ */
+
+// Atan returns the arc tangent of x.
+func Atan(x float64) float64 {
+	if x > 0 {
+		return satan(x);
+	}
+	return -satan(-x);
+}