• Josh Bleecher Snyder's avatar
    runtime: speed up fastrand() % n · 46a75870
    Josh Bleecher Snyder authored
    This occurs a fair amount in the runtime for non-power-of-two n.
    Use an alternative, faster formulation.
    
    name           old time/op  new time/op  delta
    Fastrandn/2-8  4.45ns ± 2%  2.09ns ± 3%  -53.12%  (p=0.000 n=14+14)
    Fastrandn/3-8  4.78ns ±11%  2.06ns ± 2%  -56.94%  (p=0.000 n=15+15)
    Fastrandn/4-8  4.76ns ± 9%  1.99ns ± 3%  -58.28%  (p=0.000 n=15+13)
    Fastrandn/5-8  4.96ns ±13%  2.03ns ± 6%  -59.14%  (p=0.000 n=15+15)
    
    name                    old time/op  new time/op  delta
    SelectUncontended-8     33.7ns ± 2%  33.9ns ± 2%  +0.70%  (p=0.000 n=49+50)
    SelectSyncContended-8   1.68µs ± 4%  1.65µs ± 4%  -1.54%  (p=0.000 n=50+45)
    SelectAsyncContended-8   282ns ± 1%   277ns ± 1%  -1.50%  (p=0.000 n=48+43)
    SelectNonblock-8        5.31ns ± 1%  5.32ns ± 1%    ~     (p=0.275 n=45+44)
    SelectProdCons-8         585ns ± 3%   577ns ± 2%  -1.35%  (p=0.000 n=50+50)
    GoroutineSelect-8       1.59ms ± 2%  1.59ms ± 1%    ~     (p=0.084 n=49+48)
    
    Updates #16213
    
    Change-Id: Ib555a4d7da2042a25c3976f76a436b536487d5b7
    Reviewed-on: https://go-review.googlesource.com/36932
    Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
    Reviewed-by: 's avatarBrad Fitzpatrick <bradfitz@golang.org>
    Reviewed-by: 's avatarKeith Randall <khr@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    46a75870
rand_test.go 787 Bytes