Some consumer stumbled upon EC_POINT_{add,dbl} being faster with a
"custom" P-224 curve than the built-in one and made "custom" clones to
work around this. Before the EC_FELEM refactor, EC_GFp_nistp224_method
used BN_mod_mul for all reductions in fallback point arithmetic (we
primarily support the multiplication functions and keep the low-level
point arithmetic for legacy reasons) which took quite a performance hit.
EC_FELEM fixed this, but standalone felem_{mul,sqr} calls out of
nistp224 perform a lot of reductions, rather than batching them up as
that implementation is intended. So it is still slightly faster to use a
"custom" curve.
Custom curves are the last thing we want to encourage, so just route the
tuned implementations out of EC_METHOD to close this gap. Now the
built-in implementation is always solidly faster than (or identical to)
the custom clone. This also reduces the number of places where we mix
up tuned vs. generic implementation, which gets us closer to making
EC_POINT's representation EC_METHOD-specific.
Change-Id: I843e1101a6208eaabb56d29d342e886e523c78b4
Reviewed-on: https://boringssl-review.googlesource.com/c/32848
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
cfd50c63a1