FW: Literal overflow test fails
simonpj at microsoft.com
Mon Aug 19 10:40:35 CEST 2013
Could you act on this thread please? Currently I think the Windows build is broken because of it.
I think Ian is right, namely that the way to get a particular bit-pattern with type 'Int' is to use fromIntegral. But it needs a comment to explain the idiom.
eg try compiling this with -O:
foo :: Int32
foo = fromIntegral (0x80000000 :: Word32) :: Int32
Foo.foo = GHC.Int.I32# (-2147483648)
From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Ian Lynagh
Sent: 05 August 2013 16:34
To: ghc-devs at haskell.org
Subject: Re: Literal overflow test fails
On Sat, Aug 03, 2013 at 09:47:07PM +0000, Simon Peyton-Jones wrote:
> libraries\Win32\Graphics\Win32\GDI\HDC.hs:145:14: Warning:
> Literal 2147483648 of type Int overflows
> The offending code is:
> setTextCharacterExtra dc extra =
> failIf (== 0x80000000) "SetTextCharacterExtra" $
> c_SetTextCharacterExtra dc extra
> - should we use minBound here?
The spec defines the failure value as 0x80000000, so it would be better
to use that constant:
I had a similar problem with a 0xdeadbeef constant in the compiler
source. I changed it to be
fromIntegral (0xdeadbeef :: Word32)
instead. I'd suggest doing similarly for the 0x80000000.
> - what should the new literal-overlflow code do for 0xblah constants?
In my opinion, it's doing the right thing.
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