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formatRealFloat rounds numbers differently than Numeric counterparts #105

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RyanGlScott opened this issue Dec 11, 2014 · 1 comment
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formatRealFloat rounds numbers differently than Numeric counterparts #105

RyanGlScott opened this issue Dec 11, 2014 · 1 comment

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@RyanGlScott
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Using formatRealFloat from Data.Text.Lazy.Builder.RealFloat on GHC 7.8.3 sometimes rounds decimals differently than the show*Float functions from Numeric. An example:

> showGFloat (Just 4) (0.12345 :: Float) ""
"0.1234"
> formatRealFloat Generic (Just 4) (0.12345 :: Float)
"0.1235"

Upon a quick glance, it looks like this discrepancy is caused by the roundTo function in Data.Text.Internal.Builder.RealFloat.Functions. The implementation seems to be based off of the identically named function roundTo in GHC.Float (at least, up to base-4.5.1.0). In base-4.6.0.0, however, the implementation of roundTo was changed, which would expain the different results.

Perhaps using CPP pragmas to produce the correct implementation of roundTo depending on which version of base is being used would fix this problem?
bos added a commit that referenced this issue Dec 12, 2014
@bos
Add a (failing) QuickCheck test for formatRealFloat (gh-105)
789c63f
bos added a commit that referenced this issue Dec 12, 2014
@bos
Update roundTo to correspond to base-4.6.0.0 changes (gh-105)
7e66b81
bos added a commit that referenced this issue Dec 12, 2014
@bos
Further generalise the formatRealFloat tests (gh-105)
4f7664a
@bos
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bos commented Dec 12, 2014

Thanks. I've released the fix as 1.2.0.3.

@bos bos closed this as completed Dec 12, 2014
jsonn pushed a commit to jsonn/pkgsrc that referenced this issue Dec 13, 2014
Update to 1.2.0.3
aa2d368 
changelog:
1.2.0.3

* Update formatRealFloat to correspond to the definition in versions
  of base newer than 4.5 (haskell/text#105)
bos added a commit that referenced this issue Feb 18, 2015
@bos
Add a (failing) QuickCheck test for formatRealFloat (gh-105)
b1c6756
bos added a commit that referenced this issue Feb 18, 2015
@bos
Update roundTo to correspond to base-4.6.0.0 changes (gh-105)
5902ed0
bos added a commit that referenced this issue Feb 18, 2015
@bos
Further generalise the formatRealFloat tests (gh-105)
74f55aa
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@bos @RyanGlScott