add numerical recipes library

lib/nr/cpp/recipes/hunt.cpp

@@ -0,0 +1,53 @@
+#include "nr.h"
+
+void NR::hunt(Vec_I_DP &xx, const DP x, int &jlo)
+{
+	int jm,jhi,inc;
+	bool ascnd;
+
+	int n=xx.size();
+	ascnd=(xx[n-1] >= xx[0]);
+	if (jlo < 0 || jlo > n-1) {
+		jlo=-1;
+		jhi=n;
+	} else {
+		inc=1;
+		if (x >= xx[jlo] == ascnd) {
+			if (jlo == n-1) return;
+			jhi=jlo+1;
+			while (x >= xx[jhi] == ascnd) {
+				jlo=jhi;
+				inc += inc;
+				jhi=jlo+inc;
+				if (jhi > n-1) {
+					jhi=n;
+					break;
+				}
+			}
+		} else {
+			if (jlo == 0) {
+				jlo=-1;
+				return;
+			}
+			jhi=jlo--;
+			while (x < xx[jlo] == ascnd) {
+				jhi=jlo;
+				inc <<= 1;
+				if (inc >= jhi) {
+					jlo=-1;
+					break;
+				}
+				else jlo=jhi-inc;
+			}
+		}
+	}
+	while (jhi-jlo != 1) {
+		jm=(jhi+jlo) >> 1;
+		if (x >= xx[jm] == ascnd)
+			jlo=jm;
+		else
+			jhi=jm;
+	}
+	if (x == xx[n-1]) jlo=n-2;
+	if (x == xx[0]) jlo=0;
+}