feat: add splitmix hash to hashmap

Author: a1fredbao

src/alfred/data_structure/hashmap.hpp

@@ -1,6 +1,7 @@
 #ifndef AFDS_HASHMAP
 #define AFDS_HASHMAP
 
+#include "splitmix.hpp"
 #include <utility>
 #include <vector>
 
@@ -12,6 +13,7 @@ struct HashMap { // HashMap for integer keys.
         V val;
         u32 ne;
     };
+    Splitmix<K> hash;
     u32 lim, mask, tot;
     std::vector<u32> fi;
     std::vector<Node> e;
@@ -22,7 +24,7 @@ struct HashMap { // HashMap for integer keys.
         mask = lim - 1, e.resize(sz);
     }
     inline void inc(K x, V delta) {
-        u32 u = x & mask;
+        u32 u = hash(x) & mask;
         for (u32 i = fi[u]; i; i = e[i].ne) {
             if (e[i].key == x) {
                 e[i].val += delta;
@@ -32,7 +34,7 @@ struct HashMap { // HashMap for integer keys.
         e[++tot] = {x, V() + delta, fi[u]}, fi[u] = tot;
     }
     inline void set(K x, V v) {
-        u32 u = x & mask;
+        u32 u = hash(x) & mask;
         for (u32 i = fi[u]; i; i = e[i].ne) {
             if (e[i].key == x) {
                 e[i].val = v;
@@ -43,15 +45,15 @@ struct HashMap { // HashMap for integer keys.
     }
     // this method does not create new element, returns V() by default.
     inline V get(K x) {
-        u32 u = x & mask;
+        u32 u = hash(x) & mask;
         for (u32 i = fi[u]; i; i = e[i].ne) {
             if (e[i].key == x) return e[i].val;
         }
         return V();
     }
     // this method creates new element.
     inline V &operator[](K x) {
-        u32 u = x & mask;
+        u32 u = hash(x) & mask;
         for (u32 i = fi[u]; i; i = e[i].ne) {
             if (e[i].key == x) return e[i].val;
         }

src/alfred/data_structure/splitmix.hpp

@@ -0,0 +1,21 @@
+#ifndef AFDS_SPLITMIX
+#define AFDS_SPLITMIX
+
+template <class T>
+struct Splitmix {
+    inline T operator()(T x) {
+        if constexpr (sizeof(T) == 8) {
+            T z = (x += 0x9e3779b97f4a7c15);
+            z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+            z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+            return z ^ (z >> 31);
+        } else {
+            T z = (x += 0x9e3779b9);
+            z = (z ^ (z >> 16)) * 0x85ebca6b;
+            z = (z ^ (z >> 13)) * 0xc2b2ae35;
+            return z ^ (z >> 16);
+        }
+    }
+};
+
+#endif