add numerical recipes library

lib/nr/k_and_r/recipes/locate.c

@@ -0,0 +1,22 @@
+
+void locate(xx,n,x,j)
+float x,xx[];
+unsigned long *j,n;
+{
+	unsigned long ju,jm,jl;
+	int ascnd;
+
+	jl=0;
+	ju=n+1;
+	ascnd=(xx[n] >= xx[1]);
+	while (ju-jl > 1) {
+		jm=(ju+jl) >> 1;
+		if (x >= xx[jm] == ascnd)
+			jl=jm;
+		else
+			ju=jm;
+	}
+	if (x == xx[1]) *j=1;
+	else if(x == xx[n]) *j=n-1;
+	else *j=jl;
+}