Need Help Turning Into Stored Function

[Caleb Guenther]

I'd like to turn the following function into a MySQL stored function, but I'm fairly new to the concept:

int getCharacterLevel(int numXP)
{
int level = 1;
while (numXP > 4 + level)
numXP -= 4 + level++;
return level;
}

And then I would like to call it with php like

print mysql_result("SELECT getCharacterLevel(COUNT(XP)) FROM tbl_characters", 0);

Any ideas?