Identify which parameters were passed to a procedure (Oracle)
So the way I do this is I don't use default values. Or rather, I set them to NULL as default. Then within my procedure body I check to see if it's equal to NULL and if so set it to a sane default. At that point you could mangle a flag or two in the same space to see what's being set or not set.

However, there's the edge case of if they intended to pass in NULL for some reason. However, most devs don't deal well with tripletcase, so I don't usually worry about that (additionally, if I'm passing in a value, I need to pass a value, not null, so null for me means never-was-defined)