Re: Enabling Checksums

On Wed, 2013-03-20 at 02:11 +0200, Ants Aasma wrote:
> Fletcher is also still a strong contender, we just need to replace the
> 255 modulus with something less prone to common errors, maybe use
> 65521 as the modulus. I'd have to think how to best combine the values
> in that case. I believe we can lose the property that neither byte can
> be zero, just avoiding both being zero seems good enough to me.

Agreed on all points.

I've been following your analysis and testing, and it looks like there
are still at least three viable approaches:

1. Some variant of Fletcher
2. Some variant of CRC32
3. Some SIMD-based checksum

Each of those has some open implementation questions, as well. If we
settle on one of those approaches, we don't necessarily need the fastest
implementation right away. I might even argue that the first patch to be
committed should be a simple implementation of whatever algorithm we
choose, and then optimization should be done in a separate patch (if it
is tricky to get right).

Of course, it's hard to settle on the general algorithm to use without
knowing the final performance numbers. So right now I'm in somewhat of a
holding pattern until we settle on something.

Regards,
Jeff Davis