We have a ton of per-file rotation functions, often with generic names
that do not tell you whether they are uint32_t vs uint64_t, or rotl vs
rotr.
Additionally, (x >> r) | (x << (32 - r)) is UB at r = 0.
(x >> r) | (x << ((-r) & 31)) works for 0 <= r < 32, which is what
cast.c does. GCC and Clang recognize this pattern as a rotate, but MSVC
doesn't. MSVC does, however, provide functions for this.
We usually rotate by a non-zero constant, which makes this moot, but
rotation comes up often enough that it's worth extracting out. Some
particular changes to call out:
- I've switched sha256.c from rotl to rotr. There was a comment
explaining why it differed from the specification. Now that we have
both functions, it's simpler to just match the specification.
- I've dropped all the inline assembly from sha512.c. Compilers should
be able to recognize rotations in 2021.
Change-Id: Ia1030e8bfe94dad92514ed1c28777447c48b82f9
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/49765
Reviewed-by: Adam Langley <agl@google.com>
Adam Langley
David Benjamin