Do we need an unsigned multiplyHigh? (original) (raw)

Peter Lawrey peter.lawrey at gmail.com
Wed Sep 27 15:25:32 UTC 2017

Indeed cleanliness is in the eye of the beholder. ;) I feel for mathematical code like this it should be possible to write something as fast and clear as C++, whether that is desirable or not is another matter.

Perhaps project Valhalla will be a way to return multiple values by having a composite value type, or panama with it's support for XMM instructions (or both)

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On 27 September 2017 at 16:44, Andrew Haley <aph at redhat.com> wrote:

On 27/09/17 11:28, Peter Lawrey wrote: > If you need multiplyHigh for 128-bit then you need uint256. At some point > you have to decide whether you need that many bits as a supported > operation. When Java was created a 64-bit long as the widest type made > sense, however CPUs such as x64 now support 128, 256 and 512 bit natively > and having the JVM dong its best to work this out is not as clean as > defining it explicitly.

I guess cleanliness is in the eye of the beholder. IMO multiplyHigh is as clean as we need, and I'd rather see more complexity there than in the type system. It'd be nice to be able to return more than one scalar value from a method, for sure. -- Andrew Haley Java Platform Lead Engineer Red Hat UK Ltd. <https://www.redhat.com> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671

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