SVN=114204

src/lib/math/log.go

@@ -0,0 +1,70 @@
+// 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 log
+
+import	sys "sys"
+export	log, log10
+
+/*
+	log returns the natural logarithm of its floating
+	point argument.
+
+	The coefficients are #2705 from Hart & Cheney. (19.38D)
+
+	It calls frexp.
+*/
+
+const
+(
+	log2	=   .693147180559945309e0;
+	ln10o1	=   .4342944819032518276511;
+	sqrto2	=   .707106781186547524e0;
+	p0	=  -.240139179559210510e2;
+	p1	=   .309572928215376501e2;
+	p2	=  -.963769093377840513e1;
+	p3	=   .421087371217979714e0;
+	q0	=  -.120069589779605255e2;
+	q1	=   .194809660700889731e2;
+	q2	=  -.891110902798312337e1;
+)
+
+func
+log(arg double) double
+{
+	var x, z, zsq, temp double;
+	var exp int;
+
+	if arg <= 0 {
+		return sys.NaN();
+	}
+
+	exp,x = sys.frexp(arg);
+	for x < 0.5 {
+		x = x*2;
+		exp = exp-1;
+	}
+	if x < sqrto2 {
+		x = x*2;
+		exp = exp-1;
+	}
+
+	z = (x-1) / (x+1);
+	zsq = z*z;
+
+	temp = ((p3*zsq + p2)*zsq + p1)*zsq + p0;
+	temp = temp/(((zsq + q2)*zsq + q1)*zsq + q0);
+	temp = temp*z + double(exp)*log2;
+	return temp;
+}
+
+func
+log10(arg double) double
+{
+
+	if arg <= 0 {
+		return sys.NaN();
+	}
+	return log(arg) * ln10o1;
+}