... or even as a one liner, like in the test
return Math.multiplyHigh(x, y) + ((x >> (Long.SIZE - 1)) & y) + ((y >>
(Long.SIZE - 1)) & x);
On 2021-07-02 13:08, Andrew Dinn wrote:
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
