add numerical recipes library

lib/nr/ansi/recipes/gasdev.c

@@ -0,0 +1,26 @@
+
+#include <math.h>
+
+float gasdev(long *idum)
+{
+	float ran1(long *idum);
+	static int iset=0;
+	static float gset;
+	float fac,rsq,v1,v2;
+
+	if (*idum < 0) iset=0;
+	if  (iset == 0) {
+		do {
+			v1=2.0*ran1(idum)-1.0;
+			v2=2.0*ran1(idum)-1.0;
+			rsq=v1*v1+v2*v2;
+		} while (rsq >= 1.0 || rsq == 0.0);
+		fac=sqrt(-2.0*log(rsq)/rsq);
+		gset=v1*fac;
+		iset=1;
+		return v2*fac;
+	} else {
+		iset=0;
+		return gset;
+	}
+}