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Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values |
Date: |
Tue, 17 Nov 2015 16:47:29 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Laszlo Ersek <address@hidden> writes:
> I accept this is a defensible, maybe even reasonable choice to make in
> the QEMU project. On the other hand, I personally cannot stop hating
> shifting negative values (any direction) -- indeed, the *original* code
> from <https://github.com/madler/zlib/pull/112> makes me barf too.
>
> Therefore,
>
> Grudgingly-reviewed-by: Laszlo Ersek <address@hidden>
>
> (I realize the flag for the pointer wraparound has been separated; this
> is strictly about shifts.)
What's so abhorrent about shifting negative values? I know machines
with signed integer representations other than twos complement exist, as
do machines that can't do both logical and arithmetic shifts. Mostly
inside computer museums, though.
C was standardized at a time when keeping the language sufficiently
loose to permit efficient implementation on these oddball machines made
a lot more sense than it does now. Making it undefined behavior went
too far, though. Implementation-defined or unspecified behavior would
have sufficed.
Learn to stop worrying and love the signed shifts :)
- [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Markus Armbruster, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Paolo Bonzini, 2015/11/17
- Re: [Qemu-devel] [PATCH v2 for 2.5] QEMU does not care about left shifts of signed negative values, Peter Maydell, 2015/11/17