Re: js/drop-mingw-test-cmp, was Re: What's cooking in git.git (Dec 2022, #03; Sun, 11)

> Logged the sizes of files handed to test_cmp (on macOS).  19170 calls,
> median size 42 bytes, average size 617 bytes.  2307 calls with empty
> files, 1093 of which in t1092 alone.  The two biggest files in t1050,
> 2000000 and 2500000 bytes.  t9300 in third place with 180333, one
> magnitude smaller.
>
> t1050 at 8a4e8f6a67 (The second batch, 2022-12-26) on Windows:
>
> Benchmark 1: sh.exe t1050-large.sh
>   Time (mean ± σ):     18.312 s ±  0.069 s    [User: 0.000 s, System: 0.003 s]
>   Range (min … max):   18.218 s … 18.422 s    10 runs
>
> ... and with the patch:
>
> Benchmark 1: sh.exe t1050-large.sh
>   Time (mean ± σ):      5.709 s ±  0.046 s    [User: 0.000 s, System: 0.003 s]
>   Range (min … max):    5.647 s …  5.787 s    10 runs
>
> So it works as advertised for big files, but calling an external
> program 19000 times takes time as well, which explain the longer
> overall test suite duration.
>
> If we use test_cmp_bin for the two biggest comparisons we get the
> same speedup:
>
> Benchmark 1: sh.exe t1050-large.sh
>   Time (mean ± σ):      5.719 s ±  0.089 s    [User: 0.000 s, System: 0.006 s]
>   Range (min … max):    5.659 s …  5.960 s    10 runs
>
> Is this safe?  The files consist of X's and Y's at the point of
> comparison, so they aren't typical binary files, but they don't
> have line endings at all or any user-readable content, so I think
> treating them as blobs is appropriate.