basic implementation

include/bloom_filter.h

@@ -3,11 +3,66 @@
 
 #include "mem_table.h"
 
+// class BloomFilter {
+//   public:
+//     BloomFilter(int bits_per_key) : bits_per_key_(bits_per_key_) {
+//         hash_times_ = bits_per_key_ * 0.69; // ln2
+//     }
+//     void CalculateFilterTable(MemTable &immutable_memtbale, int n, std::string *dst) {
+//         size_t bits = n * bits_per_key_;
+//         if (bits < 64)
+//             bits = 64;
+//         size_t bytes = (bits + 7) / 8;
+//         bits = bytes * 8;
+//         dst->resize(bytes, 0);
+//     }
+
+//     bool KeyMayExist(const std::string &key, const std::string &filter);
+
+//   private:
+//     int bits_per_key_;
+//     int hash_times_;
+// };
+
 class BloomFilter {
   public:
-    BloomFilter(int bits_per_key);
-    void CalculateFilterTable(MemTable immutable_memtbale, std::string* dst);
-    bool KeyMayExist(const std::string& key, const std::string& filter);
+    static void CalculateFilterTable(MemTable &immutable_memtbale, std::string *dst) {
+        dst->resize(sizeof(size_t), 0);
+
+        char *array = &(*dst)[0];
+        int char_num = dst->size() / sizeof(char);
+
+        size_t hash_table;
+        for (immutable_memtbale.ReachBegin(); immutable_memtbale.Curr(); immutable_memtbale.Next()) {
+            size_t hash_code = hash_algorithm_(immutable_memtbale.Curr()->GetKey());
+            char *hash_code_byte = (char *)&hash_code;
+            for (int i = 0; i < char_num; i++) {
+                array[i] |= hash_code_byte[i];
+            }
+        }
+    }
+
+    static bool KeyMayExist(std::string &key, std::string &filter) {
+        if (filter.size() != sizeof(size_t))
+            return false;
+
+        char *array = &(filter)[0];
+        int char_num = filter.size() / sizeof(char);
+
+        size_t hash_code = hash_algorithm_(key);
+        char *hash_code_byte = (char *)&hash_code;
+
+        for (int i = 0; i < char_num; i++) {
+            if ((array[i] ^ hash_code_byte[i]) != hash_code_byte[i]) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+  private:
+    static std::hash<std::string> hash_algorithm_;
 };
 
 #endif