Commits on Jun 21, 2024

1. aes-gcm: Clarify CPU feature detection. …

   Although every key has been represented with the same types
   `aes::AES_KEY` and `gcm::HTable` regardless of which implementation is
   used, in reality those types are polymorphic in ways that aren't
   captured by the type system currently. Thus, the
   `set_encrypt_key!` function must be matched with the corresponding
   `encrypt_block!` and/or `ctr32_encrypt_blocks!` function. Previously,
   we did CPU feature detection for each function call and assumed that
   CPU feature detection is idempotent. Now, we do CPU feature detection
   during key construction and make the lesser assumption that at least
   those same CPU features are available as long as the key exists.
   
   This is a step towards making further improvements in CPU-feature-based
   dispatching.
   
   This makes code coverage reporting a little clearer. For example, it
   became clearer that the x86 VPAES implementation wasn't being tested in
   CI; this will be rectified in another commit.
   
   One side-effect of this change is that GCM keys (and thus AES-GCM keys)
   are now much smaller on targets that don't support any assembly
   implementation, as they now just store a single `U128` instead of a
   whole `HTable`.
   
   Another nice effect is that the dead ctr32_encrypt_blocks
   implementation for aarch64 is no longer needed.
   
   ```
   git difftool HEAD^1:src/aead/aes.rs src/aead/aes/bs.rs
   git difftool HEAD^1:src/aead/aes.rs src/aead/aes/vp.rs
   ```

   

   briansmith committed Jun 21, 2024
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