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Re: Negative shift counts

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On 21/04/15 11:33, Noob wrote:
> Hello,
> 
> I am aware that negative shift counts have undefined behavior.
> 
>   int i = 40 << -2; // UB
> 
> It seems to me that a natural way to extend shift counts to
> negative values would be to just flip the shift direction.
> 
> The above statement would behave "as if" we'd written
> 
>   int i = 40 >> 2;
> 
> 
> I suppose negative shift counts were unsupported in the original
> language definition (?) in the 70s and remained unsupported in the
> first edition of K&R C? Perhaps this was done to save space when
> RAM was tight, and such a "feature" was not considered to bring
> any value?
> 
> Then ANSI saw no benefit to discuss defining the behavior during
> the standardization process in the 80s? Because no implementation
> offered this as an extension?
> 
> I'm perplexed, because it seems to be a trivial extension, with
> low complexity, for a small gain in expressiveness.
> 
> Do you see perhaps other ways to define the behavior of negative
> shift counts that would be at odds with the one proposed above?
> 
> Regards.

The conversion between shift directions is trivial when the shift count
is constant - much less so when it is variable.

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Negative shift counts Noob <root@127.0.0.1> - 2015-04-21 11:33 +0200
  Re: Negative shift counts David Brown <david.brown@hesbynett.no> - 2015-04-21 12:22 +0200
    Re: Negative shift counts Noob <root@127.0.0.1> - 2015-04-21 13:12 +0200
  Re: Negative shift counts Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-21 12:02 +0100
  Re: Negative shift counts glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-04-29 20:08 +0000

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