* optimization: faster ISQRT on fixnums and small bignums
* optimization: faster and smaller INTEGER-LENGTH on fixnums on x86-64.
* optimization: On x86-64, the number of multi-byte NOP instructions used
* optimization: faster ISQRT on fixnums and small bignums
* optimization: faster and smaller INTEGER-LENGTH on fixnums on x86-64.
* optimization: On x86-64, the number of multi-byte NOP instructions used