Re: [dpdk-dev] [PATCH v4 3/5] hash: add fallback to software CRC32 implementation

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Nov 19, 2014 at 05:35:51PM +0600, Yerden Zhumabekov wrote:
> 
> 19.11.2014 16:16, Bruce Richardson пишет:
> > On Tue, Nov 18, 2014 at 04:36:24PM -0500, Neil Horman wrote:
> >> an alternate option would be to not use the intrinsic, and craft some explicit
> >> __asm__ statement that executes the right sse42 instructions.  That way the asm
> >> is directly emitted, without requiring the -msse42 flag at all, and it will just
> >> work in all the files that call it.
> >>
> > I really don't like that approach. I think using intrinsics is much more 
> > maintainable.
> >
> 
> static inline uint32_t
> crc32_sse42_u32(uint32_t data, uint32_t init_val)
> {
> /*··__asm__ volatile(
> ············"crc32l %[data], %[init_val];"
> ············: [init_val] "+r" (init_val)
> ············: [data] "rm" (data));
> ····return init_val;*/
> 
> But wait, will __builtin_ia32_crc32si and __builtin_ia32_crc32di
> functions do the trick? ICC has them?
If builtins work on both icc and gcc, yes, that would be a solution as it
creates non sse instructions when the target cpu doesn't support it.

> What about prototyping functions and extracting their bodies to separate
> module? Does it break anything?
> 
That would be a variant on the asm inline idea, but yes, I think that would work
too
Neil


> -- 
> Sincerely,
> 
> Yerden Zhumabekov
> State Technical Service
> Astana, KZ
> 
>