David Miller <da...@davemloft.net> writes: > If it's needed for sub_n, then yes that's a bit difficult. I was > trying to figure out ways to fabricate the needed calculations > using just subcc and addxc/addxcc but haven't come up with anything > just yet.
You could always do the two's complement of one of the operands on the fly, and then use the same add with carry instructions as in add_n. I'm thinking aloud, so I'm sorry if I get this wrong, but I think it's best to handle the unlikely case of low zero limbs up front. Then it's a plain negate of the first non-zero limb, and a plain complement for the remaining limbs; the important thing here is that the negation generates no additional carries to propagate. So compared to add_n, you just get an additional xor with -1 in the loop (and not on the loop's critical path). I can't guess whether or not that will be visible in the execution time. Regards, /Niels -- Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26. Internet email is subject to wholesale government surveillance. _______________________________________________ gmp-devel mailing list gmp-devel@gmplib.org http://gmplib.org/mailman/listinfo/gmp-devel
