#7858: Fix definitions of abs/signum for Floats/Doubles -------------------------------------+------------------------------------ Reporter: lerkok | Owner: Type: bug | Status: patch Priority: normal | Milestone: Component: libraries/base | Version: 7.6.3 Resolution: | Keywords: floating point Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Changes (by bernalex): * cc: ekmett (added) * status: new => patch Comment: I added my patches for this here per SPJ's suggestion. The signum patch does not work. I do not know why. It must be due to GHC internals, because the function itself is fine as may be verified by copying {{{ signumFix x | x == 0.0 = x | isNaN x = x | x > 0.0 = 1 | otherwise = negate 1 }}} into a file signumfix.hs and :l signumfix.hs into GHCi. signumFix (-0.0 :: Float) will now return -0.0, where Prelude.signum returns 0.0 with the same argument. Here is a core dump of me invoking my Prelude.signum after building GHC/GHCi with my patches: {{{ Prelude> abs (-0.0 :: Float) ==================== Simplified expression ==================== let { it_aqt :: GHC.Types.Float [LclId, Str=DmdType, Unf=Unf{Src=<vanilla>, TopLvl=False, Arity=0, Value=False, ConLike=False, WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 70 0}] it_aqt = GHC.Num.abs @ GHC.Types.Float GHC.Float.$fNumFloat (GHC.Num.negate @ GHC.Types.Float GHC.Float.$fNumFloat (GHC.Types.F# (__float 0.0))) } in GHC.Base.thenIO @ () @ [()] (System.IO.print @ GHC.Types.Float GHC.Float.$fShowFloat it_aqt) (GHC.Base.returnIO @ [()] (GHC.Types.: @ () (it_aqt `cast` (UnivCo representational GHC.Types.Float () :: GHC.Types.Float ~# ())) (GHC.Types.[] @ ()))) 0.0 Prelude> signum (-0.0 :: Float) ==================== Simplified expression ==================== let { it_aKQ :: GHC.Types.Float [LclId, Str=DmdType, Unf=Unf{Src=<vanilla>, TopLvl=False, Arity=0, Value=False, ConLike=False, WorkFree=False, Expandable=False, Guidance=IF_ARGS [] 70 0}] it_aKQ = GHC.Num.signum @ GHC.Types.Float GHC.Float.$fNumFloat (GHC.Num.negate @ GHC.Types.Float GHC.Float.$fNumFloat (GHC.Types.F# (__float 0.0))) } in GHC.Base.thenIO @ () @ [()] (System.IO.print @ GHC.Types.Float GHC.Float.$fShowFloat it_aKQ) (GHC.Base.returnIO @ [()] (GHC.Types.: @ () (it_aKQ `cast` (UnivCo representational GHC.Types.Float () :: GHC.Types.Float ~# ())) (GHC.Types.[] @ ()))) 0.0 }}} Please note that the abs patch works well and is likely ready to go. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7858#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler