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Simplify decimal cast logic#3264

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tustvold merged 2 commits into
apache:masterfrom
tustvold:simplify-decimal-cast-logic
Dec 4, 2022
Merged

Simplify decimal cast logic#3264
tustvold merged 2 commits into
apache:masterfrom
tustvold:simplify-decimal-cast-logic

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@tustvold

@tustvold tustvold commented Dec 3, 2022

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Which issue does this PR close?

Closes #3265

Rationale for this change

The logic was extremely complicated and hard to follow, and suffered from a lot of duplication, leading to inconsistencies such as #3224

What changes are included in this PR?

Are there any user-facing changes?

@github-actions github-actions Bot added the arrow Changes to the arrow crate label Dec 3, 2022
@tustvold tustvold marked this pull request as ready for review December 3, 2022 21:27
@tustvold

tustvold commented Dec 3, 2022

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This does represent a performance regression for decimal256 arrays, as previously the logic was incorrectly using i128 arithmetic when it should have been using i256. Correctness is more important and we're talking microseconds, so I think this is fine

@tustvold tustvold requested a review from viirya December 3, 2022 21:29

@viirya viirya left a comment

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Nice!

Comment thread arrow-cast/src/cast.rs
Comment on lines +374 to +381
(mul * v.as_()).round().to_i128().ok_or_else(|| {
ArrowError::CastError(format!(
"Cannot cast to {}({}, {}). Overflowing on {:?}",
Decimal128Type::PREFIX,
precision,
scale,
v
))

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👍

@tustvold tustvold merged commit 9f64476 into apache:master Dec 4, 2022
@ursabot

ursabot commented Dec 4, 2022

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Benchmark runs are scheduled for baseline = 09d5f02 and contender = 9f64476. 9f64476 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

@liukun4515

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This does represent a performance regression for decimal256 arrays, as previously the logic was incorrectly using i128 arithmetic when it should have been using i256. Correctness is more important and we're talking microseconds, so I think this is fine

thanks @tustvold
correctness is more important than performance.

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Decimal128 to Decimal256 Overflows

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