On Tue, 5 Apr 2022 22:05:19 GMT, Paul Sandoz <psan...@openjdk.org> wrote:
> Add support to compress bits and expand bits of `int` and `long` values, see > Hacker's Delight (2nd edition), section 7.4. > > Compressing or expanding bits of an `int` or `long` value can be composed to > enable general permutations, and the "sheep and goats" operation (SAG) see > Hacker's Delight (2nd edition), section 7.7. SAG can be used to perform a > stable binary radix sort. > > The compress and expand functionality maps efficiently to hardware > instructions, such as `PEXT` and `PDEP` on x86 hardware. Thus the > implementations can be very efficient on supporting hardware. > Intrinsification will occur in a separate PR. > > This [paper](https://arxiv.org/pdf/1706.00990.pdf) investigates the > beneficial performance impact of the `PDEP` instruction, and by extension the > `expand` method, when applied to the implementation of a bit-vector select > operation in succinct data structures (for example `select(r)` returns the > position of the `r`th 1). > > Testing-wise the approach take is three fold: > 1. Tests compared against simple implementations that are easy to read and > verify against the JDK implementations (which later will also be made > intrinsic). To compensate all tests are also run flipping the test methods > and the methods under test. > 2. Tests composed of compress and expand and vice versa. > 3. Tests with known mask patterns, whose expected values are easily derived > from the inputs. This pull request has now been integrated. Changeset: fbb09160 Author: Paul Sandoz <psan...@openjdk.org> URL: https://git.openjdk.java.net/jdk/commit/fbb09160906b4d9b0a29c8e99465f12ad16d4c88 Stats: 1031 lines in 7 files changed: 1024 ins; 5 del; 2 mod 8283892: Compress and expand bits Reviewed-by: alanb, redestad ------------- PR: https://git.openjdk.java.net/jdk/pull/8115
