On Fri, 2 Jul 2021 09:39:46 GMT, Andrew Haley <a...@openjdk.org> wrote:
>> src/java.base/share/classes/java/lang/Math.java line 1211:
>>
>>> 1209: long z1 = t >>> 32;
>>> 1210:
>>> 1211: return x1 * y1 + z1 + (z0 >>> 32);
>>
>> Suggestion:
>>
>> long result = Math.multiplyHigh(x, y);
>> if (x < 0) result += y;
>> if (y < 0) result += x;
>> return result;
>
> This is just subtracting the 2's-complement offset. I guess the idea, longer
> term, is that this be an intrinsic anyway, but if you do
> `unsignedMultiplyHigh` this way you'll utilize the existing `multiplyHigh`
> intrinsic on all platforms that have it.
You can also do that branchlessly which might prove better
long result = Math.multiplyHigh(x, y);
result += (y & (x >> 63));
result += (x & (y >> 63));
return result;
-------------
PR: https://git.openjdk.java.net/jdk/pull/4644
