[ARROW-5303] [Rust] Add SIMD vectorization of numeric casts

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Abandoned
• Affects Version/s: 0.13.0
• Component/s: Rust
• External issue URL: https://github.com/apache/arrow/issues/21767
• Assignee: Unassigned
• Reporter: Neville Dipale
• Created: 12/May/19 06:50
• Updated: 11/Jan/23 07:39
• Resolved: 29/Dec/19 22:11

Description

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 for an example implementation that's limited by the differences in lane length.