Read instance of Double is incorrect

[adamschoenemann]

Description

The Read instance for Double is completely incorrect!

Expected Behavior

That show . read = id.

Actual Behavior

It seems like the fractional part is computed wildly incorrectly. For example read "42.42" :: Double yields 66.28125. It seems the error is enlarged as the numbers grow. Here is the output of reading the doubles from 0 to 2 in increments of 0.1.

mapM_ print (Prelude.map (read . show) [0 :: Double,0.1..2] :: [Double]) 
{-- yields
0.0
0.125
0.25
0.41633363423443376
0.4440892098500627
0.5551115123125784
0.666133814775094
0.7771561172376097
1.0
1.125
1.0
1.375
1.332267629550188
1.443289932012704
1.5543122344752196
1.6653345369377353
2.8421709430404016
1.8873791418627668
1.9984014443252827
2.1094237467877983
3.5527136788005027
--}

Note that Float exhibits the same kind of erroneous behaviour, whereas the types from Data.Fixed work as expected.
I've observed this behaviour both in the eta repl and when running the code directly.

Possible Fix

I assume this must've been working before but was a regression introduced in the recent port of base-4.11.1.0.

Your Environment

• Did you install an older version of Eta/Etlas before? No
• Current Eta & Etlas version:
  • Eta Version 0.8.6b2, Git Revision 107507ceb487529370d987256a4996cd07450323
  • etlas version 1.5.1.0 compiled using version 2.1.0.0 of the etlas-cabal library
• Operating System and version: Ubuntu 18.04
• Link to your project:

[Jyothsnasrinivas]

@adamschoenemann Thanks for reporting this. On the latest master this is resolved.

There was a bug in the implementation of integerLog2IsPowerOf2# function in the integer package which has been resolved now.

Feel free to open new issues if you face anymore problems.

[adamschoenemann]

Thanks, it works now!