It is not necessary to expand the key twice for each direction,
the decrypt key can be stored in reverse simultaneously.
Likewise, there is no need to store the key length alongside the
expanded keys, this is now inferred by the key length slice.
Noteably, the key expansion benchmark assumes the key array size
is the exact size of the expanded key.
Now, the ppc64le aes asm interface is identical to the generic
asm interface. Callsites and usage is updated to reflect this.
Performance uplift on POWER9 is substantial:
name old time/op new time/op delta
Expand 167ns ± 0% 49ns ± 0% -70.55%
Change-Id: I3fdaf9c27e8860e8150d4683eb4046d97a53293a
Reviewed-on: https://go-review.googlesource.com/c/go/+/398894
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Trust: Paul Murphy <murp@ibm.com>