added tests and examples for xorshift and binomial

examples/binomial.cpp

@@ -0,0 +1,67 @@
+/* Plots the distribution histogram of the fast_binomial algorithm
+ * (spoiler alert: it's pleasingly (1/2)^N all the way :D)
+ */
+#include <iostream>
+#include <array>
+#include <atomic>
+#include <thread>
+#include <iomanip>
+
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "utils/random/fast_binomial.hpp"
+
+static constexpr unsigned B = 24;
+static thread_local FastBinomial<B> rnd;
+
+static constexpr unsigned M = 4;
+static constexpr size_t N = 1ULL << 34;
+static constexpr size_t per_thread_iters = N / M;
+
+std::array<std::atomic<uint64_t>, B> buckets;
+
+void generate()
+{
+    for(size_t i = 0; i < per_thread_iters; ++i)
+        buckets[rnd() - 1].fetch_add(1);
+}
+
+int main(void)
+{
+    struct winsize w;
+    ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
+
+    auto bar_len = w.ws_col - 20;
+
+    std::array<std::thread, M> threads;
+
+    for(auto& bucket : buckets)
+        bucket.store(0);
+
+    for(auto& t : threads)
+        t = std::thread([]() { generate(); });
+
+    for(auto& t : threads)
+        t.join();
+
+    auto max = std::accumulate(buckets.begin(), buckets.end(), (uint64_t)0,
+        [](auto& acc, auto& x) { return std::max(acc, x.load()); });
+
+    std::cout << std::fixed;
+
+    for(size_t i = 0; i < buckets.size(); ++i)
+    {
+        auto x = buckets[i].load();
+        auto rel = bar_len * x / max;
+
+        std::cout << std::setw(2) << i + 1 << " ";
+
+        for(size_t i = 0; i < rel; ++i)
+            std::cout << "=";
+
+        std::cout << " " << 100 * (double)x / N << "%" << std::endl;
+    }
+
+    return 0;
+}

examples/xorshift.cpp

@@ -0,0 +1,65 @@
+/* Plots the distribution histogram of the xorshift algorithm
+ * (spoiler alert: it's pleasingly uniform all the way :D)
+ */
+#include <iostream>
+#include <array>
+#include <atomic>
+#include <thread>
+
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "utils/random/xorshift128plus.hpp"
+
+static thread_local Xorshift128plus rnd;
+static constexpr unsigned B = 1 << 10;
+static constexpr uint64_t K = (uint64_t)(-1) / B;
+
+static constexpr unsigned M = 4;
+static constexpr size_t N = 1ULL << 34;
+static constexpr size_t per_thread_iters = N / M;
+
+std::array<std::atomic<unsigned>, B> buckets;
+
+void generate()
+{
+    for(size_t i = 0; i < per_thread_iters; ++i)
+        buckets[rnd() / K].fetch_add(1);
+}
+
+int main(void)
+{
+    struct winsize w;
+    ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
+
+    auto bar_len = w.ws_col - 20;
+
+    std::array<std::thread, M> threads;
+
+    for(auto& bucket : buckets)
+        bucket.store(0);
+
+    for(auto& t : threads)
+        t = std::thread([]() { generate(); });
+
+    for(auto& t : threads)
+        t.join();
+
+    auto max = std::accumulate(buckets.begin(), buckets.end(), 0u,
+        [](auto& acc, auto& x) { return std::max(acc, x.load()); });
+
+    std::cout << std::fixed;
+
+    for(auto& bucket : buckets)
+    {
+        auto x = bucket.load();
+        auto rel = bar_len * x / max;
+
+        for(size_t i = 0; i < rel; ++i)
+            std::cout << "=";
+
+        std::cout << " " << 100.0 * x / N * B - 100 << "%" << std::endl;
+    }
+
+    return 0;
+}

utils/random/fast_binomial.hpp

@@ -27,11 +27,9 @@ class FastBinomial
     // ------------------
     // 16 1111 -> 5 =====
 
-    static constexpr uint64_t mask = (1 << N) - 1;
+    static constexpr uint64_t mask = (1ULL << N) - 1;
 
 public:
-    FastBinomial() = default;
-
     unsigned operator()()
     {
         while(true)
@@ -44,7 +42,9 @@ public:
             auto x = random() & mask;
 
             // if we have all zeros, then we have an invalid case and we
-            // need to generate again
+            // need to generate again, we have this every (1/2)^N times
+            // so therefore we could say it's very unlikely to happen for
+            // large N. e.g. N = 32; p = 2.328 * 10^-10
             if(UNLIKELY(!x))
                 continue;
 

utils/random/xorshift128plus.hpp

@@ -1,5 +1,4 @@
-#ifndef MEMGRAPH_UTILS_RANDOM_XORSHIFT_HPP
+#pragma once
-#define MEMGRAPH_UTILS_RANDOM_XORSHIFT_HPP
 
 #include <cstdlib>
 #include <random>
@@ -25,7 +24,6 @@ public:
         // the number generated by MT can be full of zeros and xorshift
         // doesn't like this so we use MurmurHash3 64bit finalizer to
         // make it less biased
-
         s[0] = avalance(dist(gen));
         s[1] = avalance(dist(gen));
     }
@@ -56,5 +54,3 @@ private:
         return s;
     }
 };
-
-#endif