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toBigInt should round identically for Double and BigDecimal (backport #3921) #3926

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merged 1 commit into from
Mar 12, 2024

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@mergify mergify bot commented Mar 12, 2024

This is an automatic backport of pull request #3921 done by Mergify.


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Original PR Body

This very minor PR fixes a bug in Num.toBigInt(x: BigDecimal, binaryPoint: Int).

The current function gives the impression to round the input BigDecimal:

val result = (x * multiplier).rounded.toBigInt

However:

BigDecimal(1.4).rounded.toBigInt // : BigInt = 1
BigDecimal(1.5).rounded.toBigInt // : BigInt = 1
BigDecimal(1.6).rounded.toBigInt // : BigInt = 1

I'm assuming this is not the intended behaviour.

The underlying issue is with the rounded function which uses the BigDecimal's MathContext. I changed this to use setScale(0) instead.

I added a testcase for rounding positive numbers. I would've added a testcase for negative ones, but as far as I know there is no RoundingMode that replicates the rounding of Doubles there (round half to positive infinity).

Contributor Checklist

  • Did you add Scaladoc to every public function/method?
  • Did you add at least one test demonstrating the PR?
  • Did you delete any extraneous printlns/debugging code?
  • Did you specify the type of improvement?
  • Did you add appropriate documentation in docs/src?
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Type of Improvement

  • Bugfix

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  • Squash: The PR will be squashed and merged (choose this if you have no preference).

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  • Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
  • Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
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---------

Co-authored-by: Schuyler Eldridge <schuyler.eldridge@gmail.com>
Co-authored-by: Jack Koenig <koenig@sifive.com>
(cherry picked from commit b9f5703)
@mergify mergify bot added the Backport Automated backport, please consider for minor release label Mar 12, 2024
@github-actions github-actions bot added the Bugfix Fixes a bug, will be included in release notes label Mar 12, 2024
@chiselbot chiselbot merged commit 6afa406 into 5.x Mar 12, 2024
19 checks passed
@chiselbot chiselbot deleted the mergify/bp/5.x/pr-3921 branch March 12, 2024 16:14
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2 participants