add numerical recipes library

lib/nr/cpp/recipes/ran3.cpp

@@ -0,0 +1,42 @@
+#include <cstdlib>
+#include "nr.h"
+using namespace std;
+
+DP NR::ran3(int &idum)
+{
+	static int inext,inextp;
+	static int iff=0;
+	const int MBIG=1000000000,MSEED=161803398,MZ=0;
+	const DP FAC=(1.0/MBIG);
+	static Vec_INT ma(56);
+	int i,ii,k,mj,mk;
+
+	if (idum < 0 || iff == 0) {
+		iff=1;
+		mj=labs(MSEED-labs(idum));
+		mj %= MBIG;
+		ma[55]=mj;
+		mk=1;
+		for (i=1;i<=54;i++) {
+			ii=(21*i) % 55;
+			ma[ii]=mk;
+			mk=mj-mk;
+			if (mk < int(MZ)) mk += MBIG;
+			mj=ma[ii];
+		}
+		for (k=0;k<4;k++)
+			for (i=1;i<=55;i++) {
+				ma[i] -= ma[1+(i+30) % 55];
+				if (ma[i] < int(MZ)) ma[i] += MBIG;
+			}
+		inext=0;
+		inextp=31;
+		idum=1;
+	}
+	if (++inext == 56) inext=1;
+	if (++inextp == 56) inextp=1;
+	mj=ma[inext]-ma[inextp];
+	if (mj < int(MZ)) mj += MBIG;
+	ma[inext]=mj;
+	return mj*FAC;
+}