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Remove ArrayEncoding usage from Digest and delete ArrayEncoding. #1731

Merged
merged 2 commits into from
Nov 22, 2023
Merged

Remove ArrayEncoding usage from Digest and delete ArrayEncoding. #1731

merged 2 commits into from
Nov 22, 2023

Commits on Nov 22, 2023

  1. Digest: Remove repr(c) from Output union.

    @briansmith
    briansmith committed Nov 22, 2023
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  2. Remove ArrayEncoding usage from Digest and delete ArrayEncoding. 

    Note: I originally tried an alternative implementation using `flat_map` that
ended up being materially slower. To fix that performance regression I had to
make the following change:

```
     let mut output = Output([0; MAX_OUTPUT_LEN]);
     output
         .0
-        .iter_mut()
-        .zip(input.iter().copied().flat_map(|Wrapping(w)| f(w)))
+        .chunks_mut(N)
+        .zip(input.iter().copied().map(|Wrapping(w)| f(w)))
         .for_each(|(o, i)| {
-            *o = i;
+            o.copy_from_slice(&i);
         });
     output
 }
```

I verified that this generates the same assembly code as the original code
on x86-64 using Rust 1.74.0, except that there are two additional 128-bit
moves in `sha256_formta_output` to zero out the latter half of `Output`,
which was intended.
    @briansmith
    briansmith committed Nov 22, 2023
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