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Bug #19318
closedFloat#round rounds incorrectly for some cases
Description
This was discovered by @aardvark179 (Duncan MacGregor).
The following spec in spec/ruby/core/float/round_spec.rb
fails on CRuby:
ruby_bug "", ""..."3.3" do
# These numbers are neighbouring floating point numbers round a
# precise value. They test that the rounding modes work correctly
# round that value and precision is not lost which might cause
# incorrect results.
it "does not lose precision during the rounding process" do
767573.1875850001.round(5, half: nil).should eql(767573.18759)
767573.1875850001.round(5, half: :up).should eql(767573.18759)
767573.1875850001.round(5, half: :down).should eql(767573.18759)
767573.1875850001.round(5, half: :even).should eql(767573.18759)
-767573.1875850001.round(5, half: nil).should eql(-767573.18759)
-767573.1875850001.round(5, half: :up).should eql(-767573.18759)
-767573.1875850001.round(5, half: :down).should eql(-767573.18759)
-767573.1875850001.round(5, half: :even).should eql(-767573.18759)
767573.187585.round(5, half: nil).should eql(767573.18759)
767573.187585.round(5, half: :up).should eql(767573.18759)
767573.187585.round(5, half: :down).should eql(767573.18758)
767573.187585.round(5, half: :even).should eql(767573.18758)
-767573.187585.round(5, half: nil).should eql(-767573.18759)
-767573.187585.round(5, half: :up).should eql(-767573.18759)
-767573.187585.round(5, half: :down).should eql(-767573.18758)
-767573.187585.round(5, half: :even).should eql(-767573.18758)
767573.1875849998.round(5, half: nil).should eql(767573.18758)
767573.1875849998.round(5, half: :up).should eql(767573.18758)
767573.1875849998.round(5, half: :down).should eql(767573.18758)
767573.1875849998.round(5, half: :even).should eql(767573.18758)
-767573.1875849998.round(5, half: nil).should eql(-767573.18758)
-767573.1875849998.round(5, half: :up).should eql(-767573.18758)
-767573.1875849998.round(5, half: :down).should eql(-767573.18758)
-767573.1875849998.round(5, half: :even).should eql(-767573.18758)
end
end
Yet this test to the best of our knowledge is correct.
This was fixed on master by @mrkn (Kenta Murata) in https://github.com/ruby/ruby/pull/7023 (thanks!).
The question is should we backport this? I think yes.
Updated by Eregon (Benoit Daloze) over 1 year ago
- Status changed from Open to Closed
Updated by nagachika (Tomoyuki Chikanaga) about 1 year ago
- Backport changed from 2.7: UNKNOWN, 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED to 3.0: REQUIRED, 3.1: REQUIRED, 3.2: DONTNEED
I don't think the fixes for this kind of long standing bugs should not be backported to stable branches.
usa-san, what is your opinion?
Updated by usa (Usaku NAKAMURA) about 1 year ago
- Backport changed from 3.0: REQUIRED, 3.1: REQUIRED, 3.2: DONTNEED to 3.0: WONTFIX, 3.1: WONTFIX, 3.2: DONTNEED
hmmm, the potential impact it could have on existing scripts, I feel like this should be kept as a feature of sorts in stable branch...
sorry. but thanks for letting me know.
Updated by nagachika (Tomoyuki Chikanaga) about 1 year ago
- Backport changed from 3.0: WONTFIX, 3.1: WONTFIX, 3.2: DONTNEED to 3.0: WONTFIX, 3.1: WONTFIX, 3.2: WONTFIX
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