add numerical recipes library

lib/nr/ansi/recipes/expdev.c

@@ -0,0 +1,13 @@
+
+#include <math.h>
+
+float expdev(long *idum)
+{
+	float ran1(long *idum);
+	float dum;
+
+	do
+		dum=ran1(idum);
+	while (dum == 0.0);
+	return -log(dum);
+}