Replace khash with custom hash set

src/hashset.hpp

@@ -19,42 +19,49 @@
 #pragma once
 
 #include "base_types.h"
-#include "khash/khash.h"
 #include "rapidhash/rapidhash.h"
 
-KHASH_SET_INIT_INT64(hashset);
+#include <cstring>
 
+
+// Stores 64-bit hashes only, not keys. Relies on collision
+// probability being extremely low at 64-bit width.
 class HashSet
 {
+private:
+  static constexpr size_t INLINE_CAPACITY = 8;
+  static constexpr size_t INITIAL_CAPACITY = 128;
+
+private:
+  u64     _inline[INLINE_CAPACITY] = {};
+  u64    *_table    = nullptr;
+  size_t  _size     = 0;
+  size_t  _capacity = 0;
+  size_t  _mask     = 0;
+
 public:
-  HashSet()
-  {
-    _set = kh_init(hashset);
-  }
+  HashSet() = default;
 
   ~HashSet()
   {
-    kh_destroy(hashset,_set);
+    delete[] _table;
   }
 
+  HashSet(const HashSet&) = delete;
+  HashSet& operator=(const HashSet&) = delete;
+
   inline
   int
   put(const char     *str_,
       cu64             len_)
   {
-    int rv;
     u64 h;
-    khint_t key;
 
     h = rapidhash(str_,len_);
+    if(h == 0)
+      h = 1;
 
-    key = kh_put(hashset,_set,h,&rv);
-    if(rv == 0)
-      return 0;
-
-    kh_key(_set,key) = h;
-
-    return rv;
+    return _put_hash(h);
   }
 
   inline
@@ -66,11 +73,110 @@ public:
 
   inline
   int
-  size(void)
+  size(void) const
   {
-    return kh_size(_set);
+    return _size;
   }
 
 private:
-  khash_t(hashset) *_set;
+  inline
+  int
+  _put_hash(const u64 h_)
+  {
+    if(_table == nullptr)
+      {
+        for(size_t i = 0; i < _size; ++i)
+          {
+            if(_inline[i] == h_)
+              return 0;
+          }
+
+        if(_size < INLINE_CAPACITY)
+          {
+            _inline[_size++] = h_;
+            return 1;
+          }
+
+        _grow(INITIAL_CAPACITY);
+      }
+
+    // 75% was benchmarked to be best generally
+    if(((_size + 1) * 4) >= (_capacity * 3))
+      _grow(_capacity * 2);
+
+    size_t idx = h_ & _mask;
+    while(true)
+      {
+        const u64 cur = _table[idx];
+
+        if(cur == 0)
+          {
+            _table[idx] = h_;
+            ++_size;
+            return 1;
+          }
+
+        if(cur == h_)
+          return 0;
+
+        idx = ((idx + 1) & _mask);
+      }
+  }
+
+  inline
+  void
+  _grow(size_t min_capacity_)
+  {
+    size_t cap = 1;
+    u64 *table;
+    size_t mask;
+
+    while(cap < min_capacity_)
+      cap <<= 1;
+
+    table = new u64[cap]();
+    mask = cap - 1;
+
+    if(_table == nullptr)
+      {
+        for(size_t i = 0; i < _size; ++i)
+          _insert_existing(table,
+                           mask,
+                           _inline[i]);
+      }
+    else
+      {
+        for(size_t i = 0; i < _capacity; ++i)
+          {
+            const u64 h = _table[i];
+            if(h == 0)
+              continue;
+
+            _insert_existing(table,
+                             mask,
+                             h);
+          }
+
+        delete[] _table;
+      }
+
+    _table = table;
+    _capacity = cap;
+    _mask = mask;
+  }
+
+  static
+  inline
+  void
+  _insert_existing(u64    *table_,
+                   size_t  mask_,
+                   u64     h_)
+  {
+    size_t idx = h_ & mask_;
+
+    while(table_[idx] != 0)
+      idx = ((idx + 1) & mask_);
+
+    table_[idx] = h_;
+  }
 };