zeroshade opened a new pull request, #731:
URL: https://github.com/apache/arrow-go/pull/731
### Rationale for this change
Improve the bytes_to_bools implementation on ARM64 NEON with actual SIMD
instructions. The result is a ~4x throughput improvement for ARM64
### What changes are included in this PR?
Rewrote the assembly using `DUP` + `CMTST` NEON pattern.
1. ld1r {v2.8b}, [ptr] — broadcast one input byte across all 8 SIMD lanes
2. cmtst v2.8b, v2.8b, v0.8b — parallel bit-test against mask
[1,2,4,8,16,32,64,128]
3. and v2.8b, v2.8b, v1.8b — normalize 0xFF → 0x01 for valid Go bool values
4. st1 {v2.8b}, [ptr], #8 — store 8 output bools at once with post-increment
A scalar tail handles the last few bits when fewer than 8 output slots
remain.
### Are these changes tested?
All existing tests continue to pass, new tests added to further validate
- Added TestBytesToBoolsCorrectness — validates every bit position against
the reference Go implementation for sizes 1–1024 bytes
- Added TestBytesToBoolsOutlenSmaller — edge case where output is smaller
than 8× input
- Added BenchmarkBytesToBools — parametric benchmark at 64B, 256B, 1KB, 4KB,
16KB
### Are there any user-facing changes?
No, this is purely a performance optimization:
*Benchmark Results (Apple M4, darwin/arm64)*
```
baseline (scalar) optimized (NEON)
sec/op sec/op vs base
BytesToBools/bytes=64-10 82.69n 21.57n -73.91%
(p=0.008)
BytesToBools/bytes=256-10 333.60n 86.43n -74.09%
(p=0.008)
BytesToBools/bytes=1K-10 1.322µ 327.4n -75.23%
(p=0.008)
BytesToBools/bytes=4K-10 5.293µ 1.297µ -75.50%
(p=0.008)
BytesToBools/bytes=16K-10 21.343µ 5.184µ -75.71%
(p=0.008)
geomean 1.327µ 333.1n -74.90%
```
Throughput: 735 MiB/s → 2,863 MiB/s (+298%)
Zero allocations in both versions. All results statistically significant.
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