Re: [PATCH v3 1/3] siphash: add cryptographically secure hashtable function

On Wed, Dec 14, 2016 at 12:55 PM, Jason A. Donenfeld [off-list ref] wrote:

Hey Tom,

Just following up on what I mentioned in my last email...

On Wed, Dec 14, 2016 at 8:35 PM, Jason A. Donenfeld [off-list ref] wrote:

quoted

I think your suggestion for (2) will contribute to further
optimizations for (1). In v2, I had another patch in there adding
siphash_1word, siphash_2words, etc, like jhash, but I implemented it
by taking u32 variables and then just concatenating these into a
buffer and passing them to the main siphash function. I removed it
from v3 because I thought that these kind of missed the whole point.
In particular:

a) siphash24_1word, siphash24_2words, siphash24_3words, etc should
take u64, not u32, since that's what siphash operates on natively

I implemented these here:
https://git.zx2c4.com/linux-dev/commit/?h=siphash&id=4652b6f3643bdba217e2194d89661348bbac48a0

Those look good, although I would probably just do 1,2,3 words and
then have a function that takes n words like jhash. Might want to call
these dword to distinguish from 32 bit words in jhash.

Also, what is the significance of "24" in the function and constant
names? Can we just drop that and call this siphash?

Tom

This will be part of the next version of the series I submit. It's not
immediately clear that using it is strictly faster than the struct
trick though. However, I'm not yet sure why this would be.

Jason