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Make [u8]::reverse() 5x faster #41764

Merged
merged 3 commits into from May 10, 2017
Merged

Make [u8]::reverse() 5x faster #41764

merged 3 commits into from May 10, 2017

Commits on May 5, 2017

  1. Make [u8]::reverse() 5x faster 

    Since LLVM doesn't vectorize the loop for us, do unaligned reads
of a larger type and use LLVM's bswap intrinsic to do the
reversing of the actual bytes.  cfg!-restricted to x86 and
x86_64, as I assume it wouldn't help on things like ARMv5.

Also makes [u16]::reverse() a more modest 1.5x faster by
loading/storing u32 and swapping the u16s with ROT16.

Thank you ptr::*_unaligned for making this easy :)
    @scottmcm
    scottmcm committed May 5, 2017
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Commits on May 6, 2017

  1. Improve implementation approach comments in [T]::reverse()

    @scottmcm
    scottmcm committed May 6, 2017
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  2. Add reverse benchmarks for u128, [u8;3], and Simd<[f64;4]> 

    None of these are affected by e8fad32.
    @scottmcm
    scottmcm committed May 6, 2017
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