siphash: Clean up hash finalisation with posthash_final() function

The POSTAMBLE macro implements the finalisation steps of SipHash.  It
relies on some variables in the environment, including returning the final
hash value that way.  That isn't great hygeine.

In addition the PREAMBLE macro takes a length parameter which is used only
to initialize the 'b' value that's not used until the finalisation and is
also sometimes modified in a non-obvious way by the callers.

The 'b' value is always composed from the total length of the hash input
plus up to 7 bytes of "tail" data - that is the remainder of the hash input
after a multiple of 8 bytes has been consumed.

Simplify all this by replacing the POSTAMBLE macro with a siphash_final()
function which takes the length and tail data as parameters and returns the
final hash value.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

0 files changed, 0 insertions, 0 deletions