• Benedikt Rascher-Friesenhausen's avatar
    Optimise `memcmp` for speed · e10a3463
    Benedikt Rascher-Friesenhausen authored
    I saw that in other parts of the `string` module iterations over `usize` were
    used to increase iteration speed.  In this patch I apply the same logic to
    `memcmp`.  With this change I measured a 7x speedup for `memcmp` on a ~1MB
    buffer (comparing two buffers with the same content) on my machine (i7-7500U),
    but I did not do any real world benchmarking for the change.  The increase in
    speed comes with the tradeoff of both increased complexity and larger generated
    assembly code for the function.
    
    I tested the correctness of the implementation by generating two randomly filled
    buffers and comparing the `memcmp` result of the old implementation against this
    new one.
    
    I ran the tests and currently currently three of them fail:
      - netdb (fails to run)
      - stdio/rename (fails to verify)
      - unistd/pipe (fails to verify)
    
    They do so though regardless of this change, so I don't think they are related.
    e10a3463
mod.rs 11.4 KB