add for hw4

hws/hw4/rng.h

@@ -0,0 +1,15 @@
+#pragma once
+#include <stdint.h>
+
+typedef struct rng {
+    int64_t seed;
+} rng;
+
+rng *get_rng(int64_t seed);
+
+void free_rng(rng* rng);
+
+float rng_uniform(rng *rng, float a, float b);
+
+float rng_gaussian(rng *rng, float m, float s);
+