[ccan] [PATCH v2 2/2] maskn & bitops: add new modules

[David Gibson]

On Mon, Jul 14, 2014 at 04:34:46PM -0400, Cody P Schafer wrote:
> On Sat, Jul 12, 2014 at 4:10 AM, David Gibson
> <david at gibson.dropbear.id.au> wrote:
> > On Thu, Jul 10, 2014 at 08:29:32PM -0400, Cody P Schafer wrote:
> >> On Thu, Jul 10, 2014 at 7:08 AM, David Gibson
> >> <david at gibson.dropbear.id.au> wrote:
> >> > On Wed, Jul 09, 2014 at 09:49:44PM -0400, Cody P Schafer wrote:
> >> >> 'maskn' provides generation of n-bit masks from a given range.
> >> >> 'bitops' provides some generic bit operations that maskn needs.
> >> [...]
> >> >> diff --git a/ccan/bitops/bitops.c b/ccan/bitops/bitops.c
> >> >> new file mode 100644
> >> >> index 0000000..a9c233b
> >> >> --- /dev/null
> >> >> +++ b/ccan/bitops/bitops.c
> >> >> @@ -0,0 +1,10 @@
> >> >> +/* CC0 (Public Domain) - see LICENSE file for details */
> >> >> +#include <ccan/bitops/bitops.h>
> >> >> +
> >> >> +extern inline uintmax_t bit_mask_nz(unsigned bits);
> >> >> +extern inline uintmax_t bit_mask(unsigned bits);
> >> >
> >> > Hrm.. does "extern inline" actually have a well-defined portable
> >> > meeting?
> >>
> >> In c99 and later, yes. The c99 rationale (
> >> http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf ) has
> >> some details, which this stack overflow post (
> >> http://stackoverflow.com/a/6312854 ) has a textual copy of.
> >>
> >> c89, on the other hand, lacks inline and gnu89 reverses the meaning of
> >> "extern inline" and "inline".
> >>
> >> > I still think these functions are so simple they should be static
> >> > inlines, at least the builtin versions.  Not everyone has LTO.
> >>
> >> Well, I don't want these to be unconditionally inlined. I'd very much
> >> rather have the compiler decide than increase code size even when it
> >> isn't a great idea.
> >
> > But won't the builtin versions be an instruction or two?
> 
> This really depends on the architecture. And the inline+extern inline
> lets the compiler choose. I don't see a good reason to take that
> choice away (unless someone wants c89 support?)

Hrm.  Except that in the case they're not, I would have expected the
compiler to already insert a function call, rather than open-coding it
at the point where the builtin is used.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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