Messages in this thread | | | Date | Sat, 23 May 2015 11:23:36 +0200 | From | Nicholas Mc Guire <> | Subject | Re: [PATCH] locking: type cleanup when accessing fast_read_ctr |
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On Wed, 20 May 2015, Oleg Nesterov wrote:
> On 05/19, Nicholas Mc Guire wrote: > > > > I assumed it would not matter but did not see a simple way of getting it > > type clean with unsigned either mainly due to the atomic_t being int and > > val in update_fast_ctr() being passed as -1. > > Perhaps clear_fast_ctr() should have a comment to explain why it returns > "int"... even if "unsigned" should work too. > Might not be into c99 standard far enough but from reviewing 6.5/J.2 I do not see this argument here.
The "well defined modulo 2**n" behavior for unsigned int can be found stated in a few places - but not in the c99 standard for arithmetic overflow.
The "well defined overflow behavior" as far as I understand c99, *only* applies to left shift operations when overflowing - see 6.5.7 " Bitwise shift operators" -> Semantics -> 4) - further for the counter problem this well defined behavior is of little help as the sum would be wrong in both cases.
I still do not see the point in the implicit/automatic type conversion here and why that should be an advantage - could somone point me to the right c99 clauses ?
thx! hofrat
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