Is his fast spoiled by swearing and reviling?

That does not invalidate his fast, but it does detract from
his reward. The Muslim should control himself and guard his tongue against
swearing, reviling, backbiting, gossiping and other things that Allaah has
forbidden whether one is fasting or not. But when one is fasting it is more
serious and he should be more careful in preserving the integrity of his
fast, and avoid that which will harm people or be a cause of trouble, anger
and division, because the Prophet (peace and blessings of Allaah be
upon him) said: “If one if you is fasting, let him not utter obscenities on
that day or raise his voice, and if anyone reviles him or wants to pick a
fight with him, let him say ‘I am a person who is fasting.’” Agreed upon. 

And Allaah is the Source of strength. May Allaah send
blessings and peace upon our Prophet Muhammad and his family and
companions.