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Make various i256 methods const #3026

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merged 1 commit into from
Nov 5, 2022
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tustvold
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@tustvold tustvold commented Nov 5, 2022

Which issue does this PR close?

Closes #.

Rationale for this change

Help with #3025 among others

What changes are included in this PR?

Tweaks various methods to make the const

This makes use of const support for loops added stabilised in 1.46 - https://blog.rust-lang.org/2020/08/27/Rust-1.46.0.html#const-fn-improvements, which is well under our MSRV which appears to be 1.62!

Are there any user-facing changes?

No

@tustvold tustvold requested a review from viirya November 5, 2022 20:48
@github-actions github-actions bot added the arrow Changes to the arrow crate label Nov 5, 2022
Comment on lines +378 to +388
const fn split_array(vals: [u8; 32]) -> ([u8; 16], [u8; 16]) {
let mut a = [0; 16];
let mut b = [0; 16];
let mut i = 0;
while i != 16 {
a[i] = vals[i];
b[i] = vals[i + 16];
i += 1;
}
(a, b)
}
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Doesn't this have new memory allocation?

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@tustvold tustvold Nov 5, 2022

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Arrays are stack allocated, and in practice the compiler will optimise all of this away

See https://rust.godbolt.org/z/7h3czsWYa

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In fact it does a better job optimising it than the old TryInto based approach - https://rust.godbolt.org/z/f6jj3PM9c

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I see. That's good point.

@tustvold tustvold merged commit 53b7f64 into apache:master Nov 5, 2022
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ursabot commented Nov 5, 2022

Benchmark runs are scheduled for baseline = e2c4199 and contender = 53b7f64. 53b7f64 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java

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3 participants