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Optimize parsing #358

Merged
merged 9 commits into from Nov 24, 2019
Merged

Optimize parsing #358

merged 9 commits into from Nov 24, 2019

Commits on Nov 23, 2019

  1. Fix existing benchmarks 

    The #[cfg(bench)] attribute does not exist and is always false. Lets
define a feature "bench" which can be used to enable benchmarks when
building with nightly.
    @michalsrb
    michalsrb committed Nov 23, 2019
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  2. Add benchmarks for DateTime parsing and formatting

    @michalsrb
    michalsrb committed Nov 23, 2019
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  3. Accept Borrow<Item> as items 

    The parse::parse and format::format functions accepted Iterator of owned
Items. While it is sometimes convenient to pass in the owned values,
neither of the functions really need to own them, so references would
be enough. The Borrow trait allows us to pass in Iterator over values,
references, boxes, etc.

According to RFC 1105 this is a minor change, because it shouldn't break
any existing code. And chrono is in pre-1.0 version anyway.

This allows us to remove multiple cloned() calls which speeds up parsing
and formating:

 name                                                 control ns/iter  remove-cloned ns/iter  diff ns/iter   diff %  speedup
 datetime::tests::bench_datetime_from_str             712              582                            -130  -18.26%   x 1.22
 datetime::tests::bench_datetime_parse_from_rfc2822   252              244                              -8   -3.17%   x 1.03
 datetime::tests::bench_datetime_parse_from_rfc3339   242              239                              -3   -1.24%   x 1.01
    @michalsrb
    michalsrb committed Nov 23, 2019
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  4. Simplify ITEMS in FromStr implementations 

    The Item::Space calls str::trim_left and Item::Numeric also calls
str::trim_left before doing anything else, so there is no need to
have Item::Space before Item::Numeric.

Speeds up parsing:
 name                                                 remove-cloned ns/iter  simplify-from-str ns/iter  diff ns/iter   diff %  speedup
 datetime::tests::bench_datetime_from_str             582                    448                                -134  -23.02%   x 1.30
 datetime::tests::bench_datetime_parse_from_rfc2822   244                    242                                  -2   -0.82%   x 1.01
 datetime::tests::bench_datetime_parse_from_rfc3339   239                    234                                  -5   -2.09%   x 1.02
    @michalsrb
    michalsrb committed Nov 23, 2019
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  5. Reimplement scan::number 

    The original would first check that there is right amount of numeric
characters and then parsed them using the std::str::parse, which
internally checks the characters again and also checks for -/+ prefix,
which is not necessary in this case.

Since we are already going over the characters, we may as well do the
parsing ourselves. The length of the function is roughly the same and
it is faster:

 name                                                 simplify-from-str ns/iter  reimplement-number ns/iter  diff ns/iter   diff %  speedup
 datetime::tests::bench_datetime_from_str             448                        365                                  -83  -18.53%   x 1.23
 datetime::tests::bench_datetime_parse_from_rfc2822   242                        195                                  -47  -19.42%   x 1.24
 datetime::tests::bench_datetime_parse_from_rfc3339   234                        166                                  -68  -29.06%   x 1.41
    @michalsrb
    michalsrb committed Nov 23, 2019
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  6. Inline some parse related functions 

    Speedups:
 datetime::tests::bench_datetime_from_str             365                         337                       -28   -7.67%   x 1.08
 datetime::tests::bench_datetime_parse_from_rfc2822   195                         181                       -14   -7.18%   x 1.08
 datetime::tests::bench_datetime_parse_from_rfc3339   166                         142                       -24  -14.46%   x 1.17
    @michalsrb
    michalsrb committed Nov 23, 2019
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  7. Fix build with rust 1.13.0

    @michalsrb
    michalsrb committed Nov 23, 2019
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  8. Temporarily globally allow deprecated 

    The question mark will be fixed in a pending commit
    @quodlibetor
    quodlibetor committed Nov 23, 2019
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  9. Handle some semantic merge conflicts 

    Something that wasn't part of this PR: the work to support nested
`Option<[ChronoType]>` was merged without being adjusted for the no-std
support

And now there are some unused import warnings because they need to get
configged out.
    @quodlibetor
    quodlibetor committed Nov 23, 2019
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