add for hw4

hws/hw4/rngutil.h

@@ -0,0 +1,17 @@
+#include <math.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Interval {
+    size_t n_interval;
+    size_t *indexed;
+} Interval;
+
+Interval *new_interval(size_t n_int);
+
+void free_interval(Interval *x);
+
+void intervalizing(Interval *interval, size_t n, float *samples);
+
+void print_histogram(Interval *interval, size_t n, float* samples);