From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: bug in lrint [was: FW: Printing long int in C program under cygwin64]
Date: Wed, 07 Jun 2017 09:10:00 -0000 [thread overview]
Message-ID: <20170607091019.GA5971@calimero.vinschen.de> (raw)
In-Reply-To: <d252aaae-b298-6fc8-7e5b-8d8be9f27f21@redhat.com>
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On May 24 07:33, Eric Blake wrote:
> On 05/24/2017 07:00 AM, Carl Fredrik Forsberg wrote:
> > type cast lrint(-1.0) = 4294967295
>
> Now that's an interesting one - it may be that cygwin1.dll actually has
> buggy behavior in lrint(). In the source code, cygwin/math/lrint.c is
> dropping down to assembly; it could very well be that the assembly code
> is incorrectly truncating things at 32 bits (where it is just fine for
> 32-bit Cygwin, but wrong for 64-bit):
>
> long lrint (double x)
> {
> long retval = 0L;
> #if defined(_AMD64_) || defined(__x86_64__) || defined(_X86_) ||
> defined(__i386__)
> __asm__ __volatile__ ("fistpl %0" : "=m" (retval) : "t" (x) : "st");
> #elif defined(__arm__) || defined(_ARM_)
> retval = __lrint_internal(x);
> #endif
> return retval;
> }
>
> But I'm not an assembly coding expert, so perhaps someone else will spot
> the fix faster.
I just applied a patch to fix this. Using fistpl is fine and dandy for
Mingw because sizeof(long) == 4, but on 64 bit Cygwin this function
has to use fistpll to account for sizeof(long) == 8.
Thanks,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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next prev parent reply other threads:[~2017-06-07 9:10 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 12:18 FW: Printing long int in C program under cygwin64 Carl Fredrik Forsberg
2017-05-24 12:54 ` bug in lrint [was: FW: Printing long int in C program under cygwin64] Eric Blake
2017-05-24 16:53 ` Erik Bray
2017-05-24 16:57 ` Erik Bray
2017-05-24 17:40 ` Eric Blake
2017-05-24 21:19 ` Carl Fredrik Forsberg
2017-05-26 12:05 ` Erik Bray
2017-05-25 1:31 ` Steven Penny
2017-05-25 7:50 ` Steven Penny
2017-05-25 17:34 ` Brian Inglis
2017-05-25 19:25 ` Eric Blake
2017-05-26 1:53 ` Steven Penny
2017-05-26 5:01 ` Steven Penny
2017-06-07 9:10 ` Corinna Vinschen [this message]
2017-06-19 11:09 Carl Fredrik Forsberg
2017-06-20 11:22 ` Corinna Vinschen
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