Tolower() in Bulk at Speed

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  • highway

    Performance-portable, length-agnostic SIMD with runtime dispatch

    And if not, it may be possible to use unaligned loads/stores to handle the fringe in a single (final) iteration:

    It is actually feasible to write vector-style code using SIMD instructions. Yes, the SIMD ISA is more complicated because of the various accumulated extensions, but this is what we currently have. And a bit larger code size (for one final loop iteration) doesn't seem to be a big deal.

  • Singeli

    High-level interface for low-level programming

    Here's an AVX-2 implementation that assumes it can read up to 31 bytes past the end of the input:

    Requires -fno-unroll-loops as otherwise clang gets overly unroll-y; the code is fast enough. Tail is dealt with by blending the originally read value with the new one.

    (yes, that's autogenerated; from some code)

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  • rust

    Empowering everyone to build reliable and efficient software.

    A few weeks ago I optimised[0] the Rust lower/upper case conversion methods to use more SIMD features. In the end, we took a very conservative level of unrolling since we deemed it unlikely that large inputs would need case conversions.


  • wuffs

    Wrangling Untrusted File Formats Safely

    This sort of stuff is where Iterate Loops are good:

    WUFFS wants this because it demands all the checking at compile time (WUFFS code with a potential buffer overflow just won't compile), so if you need bounds checks you'll be writing them out by hand and the iterate loop often allows you to express a correct solution with no actual checks.

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