On Fri, 2 Jul 2021 09:39:46 GMT, Andrew Haley <aph@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