Mississippi Code Title 99. Criminal Procedure § 99-35-131

In case of an affirmance by the supreme court of a judgment for imprisonment, if the appellant had remained in prison pending the appeal, the time of imprisonment shall be credited to him, but if he have been on bail, the supreme court shall fix the time for the commencement of his imprisonment, under the judgment of affirmance, so as to cause him to suffer the full time of imprisonment fixed by the judgment of the court below.