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Subject:	Re: bug in lrint [was: FW: Printing long int in C program under cygwin64]
To:	cygwin AT cygwin DOT com
References:	<6f28f46906804c6f8f6b4b861e202492 AT CASMBX02 DOT oslo DOT ngi DOT no> <d252aaae-b298-6fc8-7e5b-8d8be9f27f21 AT redhat DOT com> <CAOTD34Y=0udiWCAmkyEywJA6=NrUkG-T9hqXNHWckMbgkdmn_w AT mail DOT gmail DOT com> <CAOTD34YW5KoSH3unhrHfEW7Ni8-DGOPsiXNTwn75UwOhdUfVbg AT mail DOT gmail DOT com>
From:	Eric Blake <eblake AT redhat DOT com>
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Message-ID:	<fcf6ac78-b7b2-340d-a9a5-7c75738cedac@redhat.com>
Date:	Wed, 24 May 2017 11:57:26 -0500
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From: Eric Blake <eblake AT redhat DOT com>
To: cygwin AT cygwin DOT com
Message-ID: <fcf6ac78-b7b2-340d-a9a5-7c75738cedac AT redhat DOT com>
Subject: Re: bug in lrint [was: FW: Printing long int in C program under
 cygwin64]
References: <6f28f46906804c6f8f6b4b861e202492 AT CASMBX02 DOT oslo DOT ngi DOT no>
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On 05/24/2017 11:53 AM, Erik Bray wrote:

>>> 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 =3D 0L;
>>> #if defined(_AMD64_) || defined(__x86_64__) || defined(_X86_) ||
>>> defined(__i386__)
>>>   __asm__ __volatile__ ("fistpl %0"  : "=3Dm" (retval) : "t" (x) : "st"=
);

> Actually, I take it back.  gdb/objdump (and presumably binutils in
> general) was being deceptive to me about the nature of that mov
> instruction.  And in fact the fistpl should be fistpq.  That fixes it.

Is fistpq right on 32-bit, or is this a case where we need different
assembly for 32-bit (fistpl) vs. 64-bit (fistql) to match the size of
long that we are converting to?

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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