On May 6, 2016 1:07:13 PM PDT, Sasha Levin wrote:
>On 05/04/2016 08:30 PM, H. Peter Anvin wrote:
>> On 05/04/16 15:06, John Denker wrote:
>>> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
> Beware that shifting by an amount >= the number of bits in the
> word remains Undefined Behavior.
>>
On May 6, 2016 1:07:13 PM PDT, Sasha Levin wrote:
>On 05/04/2016 08:30 PM, H. Peter Anvin wrote:
>> On 05/04/16 15:06, John Denker wrote:
>>> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
> Beware that shifting by an amount >= the number of bits in the
> word remains Undefined Behavior.
>>
On 05/04/2016 08:48 PM, Linus Torvalds wrote:
> That said, the fact that the other cases weren't changed
> (rol64/ror64/ror32) does make that argument less interesting. Unless
> there was some particular code that actively ended up using
> "rol32(..0)" but not the other cases.
Right, the others se
On 05/04/2016 08:30 PM, H. Peter Anvin wrote:
> On 05/04/16 15:06, John Denker wrote:
>> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
Beware that shifting by an amount >= the number of bits in the
word remains Undefined Behavior.
>>
>>> This construct has been supported as a rotate since
On May 4, 2016 6:20:32 PM PDT, Jeffrey Walton wrote:
>On Wed, May 4, 2016 at 7:06 PM, Andi Kleen wrote:
>> On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote:
>>> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
>>> >> Beware that shifting by an amount >= the number of bits in the
>>> >> wo
On Wed, May 4, 2016 at 7:06 PM, Andi Kleen wrote:
> On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote:
>> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
>> >> Beware that shifting by an amount >= the number of bits in the
>> >> word remains Undefined Behavior.
>>
>> > This construct has b
On Wed, May 4, 2016 at 5:30 PM, H. Peter Anvin wrote:
>
> Yes. d7e35dfa is baloney IMNSHO. All it does is produce worse code, and the
> description even says so.
>
> As I said, gcc has treated the former code as idiomatic since gcc 2, so that
> support is beyond ancient.
Well, we're *trying* to
On 05/04/16 15:06, John Denker wrote:
On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
Beware that shifting by an amount >= the number of bits in the
word remains Undefined Behavior.
This construct has been supported as a rotate since at least gcc2.
How then should we understand the story told
On 05/04/2016 04:06 PM, Andi Kleen wrote:
> gcc always converts it before it could
[make a difference].
At the moment, current versions of gcc treat the idiomatic
ror/rol code as something they support ... but older versions
do not, and future version may not.
The gcc guys have made it very clea
On Wed, May 04, 2016 at 03:06:04PM -0700, John Denker wrote:
> On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
> >> Beware that shifting by an amount >= the number of bits in the
> >> word remains Undefined Behavior.
>
> > This construct has been supported as a rotate since at least gcc2.
>
> How t
On 05/04/2016 02:56 PM, H. Peter Anvin wrote:
>> Beware that shifting by an amount >= the number of bits in the
>> word remains Undefined Behavior.
> This construct has been supported as a rotate since at least gcc2.
How then should we understand the story told in commit d7e35dfa?
Is the story wr
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