Well, the original FF1 had no MP; it just had spell 'charges' based on level. You could never cast more than 9 of a certain spell level before you had to sleep in an inn, house, or cabin. Later versions of FF1 kept the spell level attribute (for restricting use until a certain level) but switched over to MP for the actual spells cost. I think part of the original's challenge was beating stuff without spamming high level spells, especially on a long dungeon. With the MP system, you have no reason to use out-dated spells once you get the higher ones. (Why use Fire when Fire3 will do?)

Nevertheless, I left attribute/stat 5 and 6 open just for such anticipation. :)

Is it possible using fancy math to make the MP curve compatible with that idea? I submit that it is not. While you can make the higher level magic cost enough that you wouldn't have the MP to cast it more times than your level would permit, making it cost that much would make you able to cast a ton of lower-level spells. I'm not against it in principle, if the game calls for it, but to simulate FF1's system you have to limit spells of all levels, and an MP system has no way of enforcing how you spend the MPs.

That being said, you could have an MP stat that isn't really MP. Since you asked this question right after the get_digits question, I'm thinking perhaps you were suggesting that each "place" be used as charges. If that's what you mean, then yep, that would work perfectly fine for simulating FF1's system except for one issue--the final place needs to be able to go up to 9, not 2 (or 4). However, why do mod 10? We're not going to show it to the player, so use a full 4 bits per level. This will work out perfectly, and let you go to 15 charges per level if desired. To elaborate:

int get_hex_digit(int currentMP, int spellLevel)
{
return ((int) currentMP / pow(16, (spellLevel -1))) % 16;
}

Since you have 32 bits, each 4 bits represents a spell level, and this will return the hex digit representing the number of charges.

Yeah, after breaking it down, I think this works a lot better than my structure of charges. We still need a list of spells per player though.