inferno-os tree was separated from the inferno-os-android (separated from the Android driver)

1 files changed, 39 insertions, 0 deletions

diff --git a/libkern/exp.c b/libkern/exp.c
new file mode 100644
index 0000000..3098194
--- /dev/null
+++ b/libkern/exp.c
@@ -0,0 +1,39 @@
+/*
+	exp returns the exponential function of its
+	floating-point argument.
+
+	The coefficients are #1069 from Hart and Cheney. (22.35D)
+*/
+
+#include <lib9.h>
+
+#define	p0  .2080384346694663001443843411e7
+#define	p1  .3028697169744036299076048876e5
+#define	p2  .6061485330061080841615584556e2
+#define	q0  .6002720360238832528230907598e7
+#define	q1  .3277251518082914423057964422e6
+#define	q2  .1749287689093076403844945335e4
+#define	log2e  1.4426950408889634073599247
+#define	sqrt2  1.4142135623730950488016887
+#define	maxf  10000
+
+double
+exp(double arg)
+{
+	double fract, temp1, temp2, xsq;
+	int ent;
+
+	if(arg == 0)
+		return 1;
+	if(arg < -maxf)
+		return 0;
+	if(arg > maxf)
+		return Inf(1);
+	arg *= log2e;
+	ent = floor(arg);
+	fract = (arg-ent) - 0.5;
+	xsq = fract*fract;
+	temp1 = ((p2*xsq+p1)*xsq+p0)*fract;
+	temp2 = ((xsq+q2)*xsq+q1)*xsq + q0;
+	return ldexp(sqrt2*(temp2+temp1)/(temp2-temp1), ent);
+}