Hi, On 3/7/19 7:16 PM, Raffaello Giulietti wrote:
> a couple of weeks ago I tried to refactor the code assuming the > existence of unsignedMultiplyHigh() (either as some future intrinsic or > as a Java method) and a wider representations of g with either 127 or > 128 bits: > g = g1 2^64 + g0 > > with either > 2^63 <= g1 < 2^64 (128 bits) > > or > 2^62 <= g1 < 2^63 (127 bits) > > Unfortunately, the resulting code of rop() isn't any simpler. That's > because then an intermediate sum can overflow the 64 bits of a long. As > a consequence, there's need for more elaborate logic to determine > the carry and other slightly more complicated computations to assemble > the final result. All in all, the resulting code has more operations and > looks longer. Ah, I see. I agree, we still don't quite have the full set of operations that we need in Java, in particular a nice way of doing an add with carry. Thank you for the explanation. > In the meantime I got rid of the last division. There's no division at > all in the whole algorithm. Excellent. This is looking very good indeed. -- Andrew Haley Java Platform Lead Engineer Red Hat UK Ltd. <https://www.redhat.com> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
