On Tue, 7 Jan 2025 23:06:39 GMT, Chen Liang <[email protected]> wrote:
>> src/java.base/share/classes/jdk/internal/util/HexDigits.java line 204:
>>
>>> 202: */
>>> 203: public static long hex8(long i) {
>>> 204: long x = Long.expand(i, 0x0F0F_0F0F_0F0F_0F0FL);
>>
>> x86 should use pepd - but aarch64?
>
> Seems there is no good way to do so on aarch; raw shifts and going through
> VPU both seem to be slower.
On both machines I'm testing here, AArch64 and x86, vector expand isn't being
used. We do have intrinsics for `Long.expand()` on all AArch64, but they're not
always efficient.
AArch64 (all versions) can do the binary to hex string in just a few
instructions, but you won't get there via a generalized expand.
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PR Review Comment: https://git.openjdk.org/jdk/pull/22942#discussion_r3074687181
