Faster timestamp parsing (~70-90% faster)

[tustvold]

Which issue does this PR close?

Closes #.

Rationale for this change

2020-09-08              time:   [41.412 ns 41.433 ns 41.453 ns]
                        change: [-94.894% -94.888% -94.881%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  2 (2.00%) low mild
  1 (1.00%) high mild
  1 (1.00%) high severe

2020-09-08T13:42:29     time:   [45.773 ns 45.807 ns 45.840 ns]
                        change: [-91.959% -91.950% -91.941%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild

2020-09-08T13:42:29.190 time:   [46.387 ns 46.458 ns 46.534 ns]
                        change: [-91.947% -91.936% -91.925%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  4 (4.00%) high mild

2020-09-08T13:42:29.190855
                        time:   [47.343 ns 47.367 ns 47.393 ns]
                        change: [-91.397% -91.389% -91.382%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) low mild

2020-09-08T13:42:29.190855999
                        time:   [47.425 ns 47.468 ns 47.514 ns]
                        change: [-91.861% -91.851% -91.842%] (p = 0.00 < 0.05)
                        Performance has improved.

2020-09-08T13:42:29+00:00
                        time:   [57.554 ns 57.587 ns 57.623 ns]
                        change: [-32.570% -32.405% -32.206%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 17 outliers among 100 measurements (17.00%)
  1 (1.00%) high mild
  16 (16.00%) high severe

2020-09-08T13:42:29.190+00:00
                        time:   [59.645 ns 59.678 ns 59.711 ns]
                        change: [-33.385% -33.207% -33.058%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  3 (3.00%) low mild
  2 (2.00%) high mild
  1 (1.00%) high severe

2020-09-08T13:42:29.190855+00:00
                        time:   [57.440 ns 57.476 ns 57.515 ns]
                        change: [-36.681% -36.590% -36.504%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  3 (3.00%) high mild

2020-09-08T13:42:29.190855999-05:00
                        time:   [57.124 ns 57.151 ns 57.179 ns]
                        change: [-37.896% -37.674% -37.515%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe

2020-09-08T13:42:29.190855Z
                        time:   [28.680 ns 28.712 ns 28.749 ns]
                        change: [-67.723% -67.672% -67.616%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 13 outliers among 100 measurements (13.00%)
  1 (1.00%) low mild
  7 (7.00%) high mild
  5 (5.00%) high severe

What changes are included in this PR?

Are there any user-facing changes?

[jhorstmann]

Impressive results!

[alamb]

I went through the code carefully, it looks good (and very clever!) to me, nicely done @tustvold

Prior to merging this, I think it needs it needs significantly more test coverage (especially negative cases) -- previously we were relying on the chrono parser to be well tested and so don't have exhaustive tests. However, with our own parser I think we also need to add our own coverage. Maybe we can crib (borrow?) from the chrono test cases?

I agree with @jhorstmann that the reported results are very nice 🚀

[alamb]

this converts the ascii to the numeric representation, right? I am thinking that the use of wrapping sub ensures that any values like (20) that is lower than '0' will not pass this check, is that correct?

[tustvold]

Wrapping sub will just underflow harmlessly for such values, which will then fail on the check for < 9

[tustvold]

I've added some more tests, PTAL, including the chrono test cases I could find... They aren't actually all that extensive... - https://github.com/chronotope/chrono/blob/main/src/format/parse.rs#L932

[alamb]

LGTM -- thank you @tustvold

[ursabot]

Benchmark runs are scheduled for baseline = de9f826 and contender = cdb042e. cdb042e is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java