[jira] [Closed] (ARROW-5303) [Rust] Add SIMD vectorization of numeric casts

["Neville Dipale (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-5303?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Neville Dipale closed ARROW-5303.
---------------------------------
    Resolution: Abandoned

When we have cast options, we can apply better optimisations rather than SIMD. `packed_simd` also currently makes it difficult to cast between different length numeric data

> [Rust] Add SIMD vectorization of numeric casts
> ----------------------------------------------
>
>                 Key: ARROW-5303
>                 URL: https://issues.apache.org/jira/browse/ARROW-5303
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: Rust
>    Affects Versions: 0.13.0
>            Reporter: Neville Dipale
>            Priority: Minor
>
> To improve the performance of cast kernels, we need SIMD support in numeric casts.
> An initial exploration shows that we can't trivially add SIMD casts between our Arrow T::Simd types, because `packed_simd` only supports a cast between T::Simd types that have the same number of lanes.
> This means that adding casts from f64 to i64 (same lane length) satisfies the bound trait `where TO::Simd : packed_simd::FromCast<FROM::Simd>`, but f64 to i32 (different lane length) doesn't.
> We would benefit from investigating work-arounds to this limitation. Please see [github::nevi_me::arrow/\{branch:simd-cast}/../kernels/cast.rs|[https://github.com/nevi-me/arrow/blob/simd-cast/rust/arrow/src/compute/kernels/cast.rs#L601]] for an example implementation that's limited by the differences in lane length.



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