Add the test for evenly distributed numbers

random/test_even_distribution.cpp

@@ -0,0 +1,105 @@
+#include <iostream>
+
+#include <inttypes.h>
+#include <algorithm>
+
+static uint32_t rprand_state[4] = {0};
+static uint64_t rprand_seed = 0;
+
+static inline uint32_t my_rotate_left(const uint32_t x, int k)
+{
+  return (x << k) | (x >> (32 - k));
+}
+
+uint32_t my_rprand_xoshiro(uint32_t state[4])
+{
+  const uint32_t result = my_rotate_left(state[1] * 5, 7) * 9;
+  const uint32_t t = state[1] << 9;
+
+  state[2] ^= state[0];
+  state[3] ^= state[1];
+  state[1] ^= state[2];
+  state[0] ^= state[3];
+
+  state[2] ^= t;
+
+  state[3] = my_rotate_left(state[3], 11);
+
+  return result;
+}
+
+uint64_t rprand_splitmix64()
+{
+  uint64_t z = (rprand_seed += 0x9e3779b97f4a7c15);
+  z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+  z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+  return z ^ (z >> 31);
+}
+
+void setSeed(unsigned long long seed)
+{
+  rprand_seed = (uint64_t)seed; // Set SplitMix64 seed for further use
+
+  // To generate the Xoshiro128** state, we use SplitMix64 generator first
+  // We generate 4 pseudo-random 64bit numbers that we combine using their LSB|MSB
+  rprand_state[0] = (uint32_t)(rprand_splitmix64() & 0xffffffff);
+  rprand_state[1] = (uint32_t)((rprand_splitmix64() & 0xffffffff00000000) >> 32);
+  rprand_state[2] = (uint32_t)(rprand_splitmix64() & 0xffffffff);
+  rprand_state[3] = (uint32_t)((rprand_splitmix64() & 0xffffffff00000000) >> 32);
+}
+
+int getValue(int min, int max)
+{
+  return my_rprand_xoshiro(rprand_state) % (std::abs(max - min) + 1) + min;
+}
+
+double getFloat()
+{
+  return my_rprand_xoshiro(rprand_state) / (double)UINT32_MAX;
+}
+
+typedef uint32_t (*func_t)();
+#define N 100
+
+static uint32_t Rand7Naive()
+{
+  return getValue(0, N);
+}
+
+static uint32_t Rand7Float()
+{
+  return (getFloat() * N);
+}
+
+void Test(func_t rand, std::string name)
+{
+  uint64_t *buckets = new uint64_t[N];
+  for (int i = 0; i < N; i++)
+    buckets[i] = 0;
+
+  for (int i = 0; i < 100000000; i++)
+    buckets[rand()]++;
+
+  uint64_t sum = 0;
+  for (int i = 0; i < N; i++)
+    sum += buckets[i];
+
+  printf("%s\n", name.c_str());
+  for (int i = 0; i < N; i++)
+    printf("%d\t%ld\n", i, buckets[i]);
+
+  printf("sum = %ld\n\n", sum);
+
+  delete buckets;
+}
+
+int main(int argc, char const *argv[])
+{
+  setSeed((unsigned int)time(NULL));
+
+  Test(Rand7Naive, "Rand7Naive");
+  setSeed((unsigned int)time(NULL));
+  Test(Rand7Float, "Rand7Float");
+
+  return 0;
+}