Re: [PATCH] Add timegm POSIX call

On Wed, 2018-08-15 at 21:18 +0200, Freddie Chopin wrote:
> On Wed, 2018-08-15 at 11:01 -0400, Craig Howland wrote:
> > > +/* returns either 0 or 1 */
> > > +static
> > > +int
> > > +__is_leap_year (int year)
> > > +{
> > > +  return (year % 4) == 0 && ((year % 100) != 0 || (((year / 100)
> > > &
> > > 3)
> > > == (-(YEAR_BASE / 100)  & 3)));
> > 
> > How about "(year & 3) == 0" instead of the % to save time? (Should
> > not matter 
> > with a good optimizer, but it is not necessarily on.)
> 
> On the other hand % is exactly 1:1 with the intent, while binary
> operations are not.
> 
> godbolt suggests that for x86-64 "(x % 4) == 0" and "(x & 3) == 0"
> give
> exactly the same code (binary operations) when optimization is
> explicitly _disabled_ (-O0).

Same for arm-none-eabi (previously I could not find the right subpage
where arm-none-eabi) was available.

https://godbolt.org/g/MYFCkb

Regards,
FCh