| 1.2 |
| 29-Jun-2020 |
riastradh | New SSE2-based bitsliced AES implementation.
This should work on essentially all x86 CPUs of the last two decades,
and may improve throughput over the portable C aes_ct implementation
from BearSSL by
(a) reducing the number of vector operations in sequence, and
(b) batching four rather than two blocks in parallel.
Derived from BearSSL'S aes_ct64 implementation adjusted so that where
aes_ct64 uses 64-bit q[0],...,q[7], aes_sse2 uses (q[0], q[4]), ...,
(q[3], q[7]), each tuple representing a pair of 64-bit quantities
stacked in a single 128-bit register. This translation was done very
naively, and mostly reduces the cost of ShiftRows and data movement
without doing anything to address the S-box or (Inv)MixColumns, which
spread all 64-bit quantities across separate registers and ignore the
upper halves.
Unfortunately, SSE2 -- which is all that is guaranteed on all amd64
CPUs -- doesn't have PSHUFB, which would help out a lot more. For
example, vpaes relies on that. Perhaps there are enough CPUs out
there with PSHUFB but not AES-NI to make it worthwhile to import or
adapt vpaes too.
Note: This includes local definitions of various Intel compiler
intrinsics for gcc and clang in terms of their __builtin_* &c.,
because the necessary header files are not available during the
kernel build. This is a kludge -- we should fix it properly; the
present approach is expedient but not ideal.
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