Re: [PATCH] Do CRC 4 bits at a time

[Nathan Sidwell <nathan@acm.org>]

On 04/26/2017 04:52 AM, Richard Biener wrote:
> On Tue, Apr 25, 2017 at 6:47 PM, Nathan Sidwell <nathan@acm.org> wrote:

> Please use 'inline' rather than 'static inline'.

Oh, ok (must have been misled by some exiting static inline somewhere)
> 
> Did you test the patch produces the same CRCs than before?  Did you do
> any performance measurements?

Yes.
1) applied both to a random incoming checksum and random value.  A 
billion iterations showed no differences.

2) 100 million iterations show the new version slightly more than twice 
as fast.

> Otherwise looks ok to me.  I wonder why we have this "copy" at all rather
> than using libiberties xcrc32?

Hm, not entirely sure, I originally introduced crc32_string back in 
2003, which could have used libiberty's (unless perhaps at that time 
things were out of sync, so we didn't have it there?)  For some reason I 
chose not to.

But now, we commonly get the CRC of individual byte values or unsigneds, 
which the xcrc32 interface doesn't do well.  David Li broke it apart to 
make that useful in 2011.

ok with the static inline fix?

nathan

-- 
Nathan Sidwell