add numerical recipes library

lib/nr/k_and_r/recipes/ran3.c

@@ -0,0 +1,48 @@
+
+#define MBIG 1000000000
+#define MSEED 161803398
+#define MZ 0
+#define FAC (1.0/MBIG)
+
+float ran3(idum)
+long *idum;
+{
+	static int inext,inextp;
+	static long ma[56];
+	static int iff=0;
+	long mj,mk;
+	int i,ii,k;
+
+	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 < MZ) mk += MBIG;
+			mj=ma[ii];
+		}
+		for (k=1;k<=4;k++)
+			for (i=1;i<=55;i++) {
+				ma[i] -= ma[1+(i+30) % 55];
+				if (ma[i] < 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 < MZ) mj += MBIG;
+	ma[inext]=mj;
+	return mj*FAC;
+}
+#undef MBIG
+#undef MSEED
+#undef MZ
+#undef FAC