add merge sort

merge_sort/Main.cpp

@@ -1,6 +1,157 @@
+#include <chrono>
 #include <iostream>
 
-int main() {
-    std::cout << "Test\n";
-    return 0;
+long getNanos()
+{
+    return std::chrono::high_resolution_clock::now().time_since_epoch().count();
+}
+
+int intKey(const int &i) { return i; }
+
+static unsigned long seed = 0;
+
+int randomInt()
+{
+    seed = (seed * 0x5DEECE66DL + 0xBL) & 0xFFFFFFFFFFFF;
+    return static_cast<int>(seed >> 17);
 }
+
+template <typename T> T *mergeSort(const T *in, int size, int (*key)(const T &))
+{
+    T *out = new T[size];
+    for (int i = 0; i < size; ++i)
+    {
+        out[i] = in[i];
+    }
+    if (size <= 1)
+    {
+        return out;
+    }
+
+    // split
+    int sizeLeft = size / 2;
+    int sizeRight = (size + 1) / 2;
+    T *left = out;
+    T *right = out + sizeLeft;
+    left = mergeSort(left, sizeLeft, key);
+    right = mergeSort(right, sizeRight, key);
+
+    // merge
+    int rightCounter = 0;
+    int leftCounter = 0;
+    for (int i = 0; i < size; ++i)
+    {
+        if (leftCounter >= sizeLeft)
+        {
+            out[i] = right[rightCounter];
+            ++rightCounter;
+        }
+        else if (rightCounter >= sizeRight)
+        {
+
+            out[i] = left[leftCounter];
+            ++leftCounter;
+        }
+        else if (key(left[leftCounter]) < key(right[rightCounter]))
+        {
+            out[i] = left[leftCounter];
+            ++leftCounter;
+        }
+        else
+        {
+            out[i] = right[rightCounter];
+            ++rightCounter;
+        }
+    }
+    delete[] right;
+    delete[] left;
+    return out;
+}
+
+void cacheTest()
+{
+    for (int size = 512; size < 100'000'000; size *= 2)
+    {
+        printf("Cache Test with size = %9d | ", size);
+        constexpr int max = 500;
+        int *a = new int[size];
+        seed = 0;
+        for (int i = 0; i < size; i++)
+        {
+            a[i] = randomInt() % max;
+        }
+        long time = -getNanos();
+        int *b = mergeSort(a, size, intKey);
+        time += getNanos();
+        printf("%10ld ns | %7.2lf ns / entry \n", time,
+               (static_cast<double>(time) / size));
+        delete[] a;
+        delete[] b;
+    }
+}
+
+struct A
+{
+    int key;
+    char filler[32];
+};
+
+int aKey(const A &a) { return a.key; }
+
+void structTest()
+{
+    for (int size = 512; size < 100'000'000; size *= 2)
+    {
+        printf("Struct Test with size = %9d | ", size);
+        constexpr int max = 500;
+        A *a = new A[size];
+        seed = 0;
+        for (int i = 0; i < size; i++)
+        {
+            a[i].key = randomInt() % max;
+        }
+        long time = -getNanos();
+        A *b = mergeSort(a, size, aKey);
+        time += getNanos();
+        printf("%10ld ns | %7.2lf ns / entry \n", time,
+               (static_cast<double>(time) / size));
+        delete[] a;
+        delete[] b;
+    }
+}
+
+int pointerKey(int *const &a) { return *a; }
+
+void pointerTest()
+{
+    for (int size = 512; size < 100'000'000; size *= 2)
+    {
+        printf("Pointer Test with size = %9d | ", size);
+        constexpr int max = 500;
+        int **a = new int *[size];
+        seed = 0;
+        for (int i = 0; i < size; i++)
+        {
+            a[i] = new int(randomInt() % max);
+        }
+        long time = -getNanos();
+        int **b = mergeSort<int *>(a, size, pointerKey);
+        time += getNanos();
+        printf("%10ld ns | %7.2lf ns / entry \n", time,
+               (static_cast<double>(time) / size));
+        for (int i = 0; i < size; i++)
+        {
+            delete a[i];
+        }
+        delete[] a;
+        delete[] b;
+    }
+}
+
+int main()
+{
+    cacheTest();
+    structTest();
+    pointerTest();
+    return 0;
+}