diff --git a/Write-hashtable-in-php/HashTable.php b/Write-hashtable-in-php/HashTable.php
index cac2a67..e3dfcd1 100644
--- a/Write-hashtable-in-php/HashTable.php
+++ b/Write-hashtable-in-php/HashTable.php
@@ -5,6 +5,8 @@ class HashTale
 	private $size = 0;
 	private $container = null;
 	
+	private $bigPrime = 1861;
+
 	public function __construct($size=1000)
 	{
 		// 哈希表的大小
@@ -21,8 +23,26 @@ private function getItemDefine()
 		);
 		
 		return $item;
+    }
+    
+    public function hashNum($key)
+	{
+        // $key不能太长，$this->bigPrime也不能太大，不然会引起整数溢出
+
+		$hashNum = 0;
+		$keyLen = strlen($key);
+        
+        // 这里的**幂运算你也可以用位移来实现
+		for ($i=0; $i<$keyLen; $i++) {
+			$hashNum += ($this->bigPrime ** ($keyLen - ($i+1))) * ord($key[$i]);
+		}
+		
+		$hashNum = $hashNum % $this->size;
+		
+		return $hashNum;
 	}
 }
 
-$hashTable = new HashTale(2);
-var_dump($hashTable);
\ No newline at end of file
+$hashTable = new HashTale();
+
+var_dump($hashTable->hashNum('hello'));
\ No newline at end of file