Ah, in that case, you're right, it would make sense to use all 64 bits for the top limb. Still, making them all equal-sized can have benefits if you use SIMD or

Ah, in that case, you're right, it would make sense to use all 64 bits for the top limb. Still, making them all equal-sized can have benefits if you use SIMD or similar techniques to operate on them uniformly. One project of mine has been trying to work with large integers in CUDA by distributing their limbs across a warp.