add for hw4

hws/hw4/rng.c

@@ -0,0 +1,69 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include "rng.h"
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+float _rng_next_float(rng *rng) {
+    uint64_t state = (uint64_t)rng->seed;
+    
+    state = (6364136223846793005ULL * state) + 1ULL;
+    
+    rng->seed = (int64_t)state;
+
+    uint32_t high_bits = (uint32_t)(state >> 40);
+    
+    return (float)high_bits * (1.0f / 16777216.0f); 
+}
+
+rng *get_rng(int64_t seed) {
+    rng *r = (rng *)malloc(sizeof(rng));
+    if (r == NULL) {
+        return NULL;
+    }
+    r->seed = seed;
+    return r;
+}
+
+void free_rng(rng* rng) {
+    free(rng);
+}
+
+float rng_uniform(rng *rng, float a, float b) {
+    float r = _rng_next_float(rng);
+    
+    return a + r * (b - a);
+}
+
+float rng_gaussian(rng *rng, float m, float s) {
+    static int has_spare = 0;
+    static float spare;
+
+    if (has_spare) {
+        has_spare = 0;
+        return m + s * spare;
+    }
+
+    has_spare = 1;
+    float u1, u2;
+
+    do {
+        u1 = _rng_next_float(rng);
+    } while (u1 == 0.0f);
+    
+    u2 = _rng_next_float(rng);
+
+    float mag = s * sqrt(-2.0f * log(u1));
+    float z1 = mag * cos(2.0f * M_PI * u2) + m;
+    float z2 = mag * sin(2.0f * M_PI * u2);
+
+    mag = sqrt(-2.0f * log(u1));
+    z1 = mag * cos(2.0f * M_PI * u2);
+    spare = mag * sin(2.0f * M_PI * u2); 
+
+    return m + s * z1;
+}