SVN=114204

src/lib/math/exp.go

@@ -0,0 +1,54 @@
+// 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 exp
+
+import	sys "sys"
+import	floor "floor"
+export	exp
+
+/*
+	exp returns the exponential func of its
+	floating-point argument.
+
+	The coefficients are #1069 from Hart and Cheney. (22.35D)
+*/
+
+const
+(
+	p0	= .2080384346694663001443843411e7;
+	p1	= .3028697169744036299076048876e5;
+	p2	= .6061485330061080841615584556e2;
+	q0	= .6002720360238832528230907598e7;
+	q1	= .3277251518082914423057964422e6;
+	q2	= .1749287689093076403844945335e4;
+	log2e	= .14426950408889634073599247e1;
+	sqrt2	= .14142135623730950488016887e1;
+	maxf	= 10000;
+)
+
+func
+exp(arg double) double
+{
+	var x, fract, temp1, temp2, xsq double;
+	var ent int;
+
+	if arg == 0 {
+		return 1;
+	}
+	if arg < -maxf {
+		return 0;
+	}
+	if arg > maxf {
+		return sys.Inf(1);
+	}
+
+	x = arg*log2e;
+	ent = int(floor.floor(x));
+	fract = (x-double(ent)) - 0.5;
+	xsq = fract*fract;
+	temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
+	temp2 = ((xsq+q2)*xsq+q1)*xsq + q0;
+	return sys.ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent);
+}