SECTION 1. Each convict who is sentenced for a definite term of more than thirty days and less than life shall be entitled to diminish the period of his sentence under the following rules and regulations:
(a) For each full month, commencing with the first day of his arrival at a provincial or Insular jail or prison, during which he has not been guilty of a violation of discipline or any of the rules of the prison, and has labored with diligence and fidelity upon all such tasks as have been assigned to him, he shall be allowed a deduction of five days from the period of his sentence.
(b) After he has served two full years of a sentence, the deduction shall be eight days for each month thereafter.
(c) After he has served live full years of a sentence, the deduction shall be ten days for each month thereafter.
(d) After he has served ten full }:ears of his sentence, the deduction from his term shall be fifteen days for each month thereafter.