This is what I think. Others might correct it. // Sic credo (quod alii corrigant):
If I had studied, I would have passed. = Si studuissem, feliciter evasissem.
Had I studied or if I were to have studied yesterday, I would pass the exam later today. = Si heri studuissem, examen posteriùs hodie feliciter evadam (modo subjunctivo) vel evasurus sim.
I'm writing in Latin hoping for correction, and not because I'm confident in how I express myself. Latinè scribo ut ab omnibus corrigar, non quod confidenter me exprimam.