Switches currently don't profile well (if at all) - John can shed more
light on that as this came up on the compiler list a few weeks ago.
sent from my phone
On Mar 12, 2015 6:06 PM, "Peter Levart" <peter.lev...@gmail.com> wrote:
>
>
> On 03/12/2015 10:04 PM, Peter Levart wrote:
>
> ... putLongUnaligned in the style of above getLongUnaligned is more tricky
> with current code structure. But there may be a middle ground (or a sweet
> spot):
>
>
> public final void putLongUnaligned(Object o, long offset, long x) {
> if (((int) offset & 1) == 1) {
> putLongParts(o, offset,
> (byte) (x >>> 0),
> (short) (x >>> 8),
> (short) (x >>> 24),
> (short) (x >>> 40),
> (byte) (x >>> 56));
> } else if (((int) offset & 2) == 2) {
> putLongParts(o, offset,
> (short)(x >>> 0),
> (int)(x >>> 16),
> (short)(x >>> 48));
> } else if (((int) offset & 4) == 4) {
> putLongParts(o, offset,
> (int)(x >> 0),
> (int)(x >>> 32));
> } else {
> putLong(o, offset, x);
> }
> }
>
>
> ...this has the same number of branches, but less instructions. You also
> need the following two:
>
>
>
> At least on Intel (with -XX:-UseUnalignedAccesses) above code (Unaligned2)
> is not any faster then your code (Unaligned) according to a JMH
> random-access test. Neither is the reversal of if/else branches
> (Unaligned1). Unaligned3 is switch-based variant (just get) and is slowest.
> Your variant seems to be the fastest by a hair:
>
> Benchmark Mode Samples Score Score
> error Units
> j.t.UnalignedTest.getLongUnaligned avgt 5 16.375
> 0.837 ns/op
> j.t.UnalignedTest.getLongUnaligned1 avgt 5 18.340
> 0.617 ns/op
> j.t.UnalignedTest.getLongUnaligned2 avgt 5 16.784
> 0.969 ns/op
> j.t.UnalignedTest.getLongUnaligned3 avgt 5 19.634
> 0.871 ns/op
> j.t.UnalignedTest.putLongUnaligned avgt 5 15.521
> 0.589 ns/op
> j.t.UnalignedTest.putLongUnaligned1 avgt 5 16.676
> 1.042 ns/op
> j.t.UnalignedTest.putLongUnaligned2 avgt 5 16.394
> 3.028 ns/op
>
>
> Regards, Peter
>
> Peter
>
>
