• David Symonds's avatar
    sort: use fewer comparisons when choosing pivot. · 78cee8b3
    David Symonds authored
    This is based on rsc's code posted to issue 2585.
    
    Benchmark results are greatly improved:
            benchmark                old ns/op    new ns/op    delta
            BenchmarkSortString1K       564397       445897  -21.00%
            BenchmarkSortInt1K          270889       221249  -18.32%
            BenchmarkSortInt64K       26850765     21351967  -20.48%
    
    Eyeballing a sampling of the raw number of comparisons shows a drop
    on the order of 20-30% almost everywhere. The test input data that
    doesn't match that are some of sawtooth/rand/plateau distributions,
    where there is no change in the number of comparisons; that is,
    there are no situations where this makes *more* comparisons.
    
    Fixes #2585.
    
    R=iant, rsc
    CC=golang-dev
    https://golang.org/cl/7306098
    78cee8b3
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