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

[Cody P Schafer]

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?)

> I would have thought making function call would actually be as much or more code
> once you do the necessary argument marshalling.