RFR: 8188044: We need Math.unsignedMultiplyHigh [v2]

[Andrew Haley]

On 7/2/21 4:30 PM, Raffaello Giulietti wrote:
> FWIW, adinn's branchless code together with
> PR https://git.openjdk.java.net/jdk/pull/4660
> make both methods less vulnerable to timing attacks.

I doubt it, because HotSpot generates conditional select instructions for
the popular systems, at least for C2.

I guess it might on a C1-only or pure interpreter system. That certainly
might be an argument for using the shift-and-add magic. With a comment
that would be fine, as the difference in performance doesn't seem to be
worth worrying about. We're looking at sub-nanosecond throughput.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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