gsmiller commented on pull request #69:
URL: https://github.com/apache/lucene/pull/69#issuecomment-816040529
@jpountz
> +1 Let go with whichever of `arr[i] = IDENTITY_PLUS_ONE[i] * val + base`
or `arr[i] = (i+1) * val + base` runs fastest in your micro benchmark. We can
still improve things later if we find a way to trick the JVM into
auto-vectorizing this loop.
Perfect, thanks! I'm changing this back to `(i + 1) * val + base` because it
(somewhat surprisingly maybe, but I suppose this simple addition could be more
efficient than an array reference) does consistently perform slightly better in
microbenchmarks (`arraryRef == 0` is this implementation while `arrayRef == 1`
references `IDENTITY_PLUS_ONE[i]`):
```
Benchmark (arrayRef) (bitsPerValue)
(exceptionCount) (sameVal) Mode Cnt Score Error Units
PackedIntsDeltaDecodeBenchmark.pForDeltaDecoder 0 0
0 2 thrpt 20 7.915 ± 0.008 ops/us
PackedIntsDeltaDecodeBenchmark.pForDeltaDecoder 1 0
0 2 thrpt 20 7.695 ± 0.010 ops/us
```
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