Messages in this thread | | | Subject | Re: linux/bitops.h | From | Sasha Levin <> | Date | Fri, 6 May 2016 16:07:13 -0400 |
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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 at least gcc2. >> >> How then should we understand the story told in commit d7e35dfa? >> Is the story wrong? >> >> At the very least, something inconsistent is going on. There >> are 8 functions. Why did d7e35dfa change one of them but >> not the other 7? > > Yes. d7e35dfa is baloney IMNSHO. All it does is produce worse code, and the description even says so.
No, the description says that it produces worse code for *really really* ancient GCC versions.
> As I said, gcc has treated the former code as idiomatic since gcc 2, so that support is beyond ancient.
Because something works in a specific way on one compiler isn't a reason to ignore this noncompliance with the standard.
Thanks, Sasha
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