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Micro-optimize vec.with_c_str for short vectors #9352

Merged
merged 9 commits into from Sep 27, 2013
Merged

Micro-optimize vec.with_c_str for short vectors #9352

merged 9 commits into from Sep 27, 2013

Commits on Sep 27, 2013

  1. std and rustc: Convert users of c_str to use .with_c_str

    @erickt
    erickt committed Sep 27, 2013
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  2. std: removed some warnings in tests.

    @erickt
    erickt committed Sep 27, 2013
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  3. std: implement Container for CString

    @erickt
    erickt committed Sep 27, 2013
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  4. std: Add benchmarks to c_str

    @erickt
    erickt committed Sep 27, 2013
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  5. std: Micro-optimize vec.with_c_str for short vectors 

    This now makes it unsafe to save the pointer returned by .with_c_str
as that pointer now may be pointing at a stack allocated array.

I arbitrarily chose 32 bytes as the length of the stack vector, and
so it might not be the most optimal size.

before:

test c_str::bench::bench_with_c_str_long ... bench: 539 ns/iter (+/- 91)
test c_str::bench::bench_with_c_str_medium ... bench: 97 ns/iter (+/- 2)
test c_str::bench::bench_with_c_str_short ... bench: 70 ns/iter (+/- 5)

after:

test c_str::bench::bench_with_c_str_long ... bench: 542 ns/iter (+/- 13)
test c_str::bench::bench_with_c_str_medium ... bench: 53 ns/iter (+/- 6)
test c_str::bench::bench_with_c_str_short ... bench: 19 ns/iter (+/- 0)
    @erickt
    erickt committed Sep 27, 2013
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  6. std: Remove an unnecessary comment from c_str 

    The documentation for `.with_c_str()` already says that the pointer
will be deallocated before returning from the function.
    @erickt
    erickt committed Sep 27, 2013
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  7. std: Up vec.with_c_str's stack buffer to 128 

    This matches @graydon's recommendation.
    @erickt
    erickt committed Sep 27, 2013
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  8. std: add micro optimization to vec.with_c_str_unchecked 

    before:

test c_str::bench::bench_with_c_str_unchecked_long ... bench: 361 ns/iter (+/- 9)
test c_str::bench::bench_with_c_str_unchecked_medium ... bench: 75 ns/iter (+/- 2)
test c_str::bench::bench_with_c_str_unchecked_short ... bench: 60 ns/iter (+/- 9)

after:

test c_str::bench::bench_with_c_str_unchecked_long ... bench: 362 ns/iter (+/-
test c_str::bench::bench_with_c_str_unchecked_medium ... bench: 30 ns/iter (+/- 7)
test c_str::bench::bench_with_c_str_unchecked_short ... bench: 12 ns/iter (+/- 4)
    @erickt
    erickt committed Sep 27, 2013
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  9. std: simplify vec.with_c_str 

    This also fixes a bug in `vec.with_c_str_unchecked` where we
were not calling `.to_c_str_unchecked()` for long strings.
    @erickt
    erickt committed Sep 27, 2013
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