2つの日付文字列を受信し、土曜日または日曜日の週末日、その日付範囲内で発生する整数を返すPHP関数を作成します。その機能を可能な限り最適化します。
Write a PHP function that receives two date strings and returns an integer with how many weekend days, Saturday or Sunday, occur within that date range.  Optimize that function as much as possible.