refactor(aes): machine-word generic fixslice#560
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Drop the cpubits-based selection between width-specific fixslice modules in preparation for unifying both into a single width-generic implementation.
Refactor the fixslice AES implementation so the algorithm body is generic over a `Word` trait, with a single `impl Word for u32` carrying all width-specific code (row width, packing routines, bitslice/inv_bitslice). The three-pass delta-swap pipeline used by `bitslice` and `inv_bitslice` is extracted into a shared width-generic `bitslice_swaps` helper, with mask constants derived from a `Word::byte_repeat` method. Each impl now only carries the bytes-in/bytes-out routine. This is a purely mechanical refactor: no logic changes, no behavior changes, the only word width supported is still `u32`.
Add the second `Word` impl, `impl Word for u64`, which batches 4 blocks per state versus 2 for `u32`. The concrete re-exports and the hazmat helpers are gated by `target_pointer_width` via `cpubits!`, selecting `u32` on 16/32-bit targets and `u64` on 64-bit.
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This looks good to me as a general direction, though it may be some time before I can review it in detail. I'm a bit confused how this broke the build the way it did, it seems somehow with only changes to the soft backend it broke things in the NEON backend somehow? |
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This PR collapses the two fixslice impls into a single
fixslice.rsparameterized over aWordtrait that abstracts the machine-word width.I tried to structure the commits to make it clear to the reviewer that this introduces no changes to the existing implementation logic.
This PR was motivated by #559 to support larger machine-word (SIMD) implementations without introducing major duplication and maintenance burden.