fixed size integer arithmetic

[point14 at magma.ca]

Hello,

Is it possible in GMP to have the size of integers (like mpz_t) to be 
fixed in size and invariant (eg, a fixed number of bits) as well as being 
arbitrarily large?

I mean once it's declared or initialized to be of a certain size, the size 
no longer changes, and arithmetic operations (add, mul, etc) that would 
normaly grow the number would simply cause it to roll over.

Is this possible with GMP and if not, do you have suggestions?

Thanks,
Martin