Parse the temperature in reverse#11
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Starting from the end of the line, take the digits one at a time.
For example the following line:
> Seattle;-12.3
* Temperature * 10 (T) is encoded as an `i16`.
* Starting from the end, the first digit is 3. T = 3
* Skip over the dot, T = 3
* Next is 2. T = 2 * 10 + 3 = 23
* Next character could be a digit, but it could also be - or ;
In this case it is 1, so T = 1 * 100 + T = 123
* One last time, we need to check for a -, which we have, so T = -T =
-123
* Next character is guaranteed to be ; thus we have also obtained the length
of the station name.
With this change, Hyperfine reports a ~1.50 faster finish time.
Tested on a 12 core / 24 thread AMD Ryzen 5900x.
> Benchmark 1: target/release/brrr-org
Time (mean ± σ): 2.205 s ± 0.020 s [User: 42.833 s, System: 1.119 s]
Range (min … max): 2.194 s … 2.260 s 10 runs
Benchmark 2: target/release/brrr
Time (mean ± σ): 1.473 s ± 0.021 s [User: 25.448 s, System: 1.108 s]
Range (min … max): 1.452 s … 1.529 s 10 runs
Summary
target/release/brrr ran
1.50 ± 0.03 times faster than target/release/brrr-org
Owner
|
Oh interesting! Give it a try after the optimizations from #2, which already sped us up a decent amount and see if it still improves things. |
Author
|
Yes, you're right! After merging in the latest improvements, speed up is now only ~5%. My feeling is that most of the gains were in minimizing/removing the search for the semicolon. |
+ move temperature parsing code to parse_temperature
+ restore temp parsing unit tests
+ replace usize decrement with unchecked_sub() just in case, though it
doesn't seem to make any meaningful difference perf-wise.
After merging in the latest improvements, the speed up offered by this
change is no longer as significant.
```
Benchmark 1: target/release/brrr-main
Time (mean ± σ): 1.196 s ± 0.006 s [User: 19.190 s, System: 1.133 s]
Range (min … max): 1.186 s … 1.207 s 10 runs
Benchmark 2: target/release/brrr
Time (mean ± σ): 1.143 s ± 0.005 s [User: 17.915 s, System: 1.150 s]
Range (min … max): 1.135 s … 1.150 s 10 runs
Summary
target/release/brrr ran
1.05 ± 0.01 times faster than target/release/brrr-main
```
Wondering if CI failing has to do with rustfmt using a different style edition.
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The observation is that the temperature component is ~fixed length (between 3 and 5 characters).
Therefore having found the end of the line, scanning from the end, we obtain both the temperature and the location of the semicolon.
With this change, Hyperfine reports a ~1.50 faster finish time.
Tested on a 12 core / 24 thread AMD Ryzen 5900x.
Benchmark 2: target/release/brrr
Time (mean ± σ): 1.473 s ± 0.021 s [User: 25.448 s, System: 1.108 s]
Range (min … max): 1.452 s … 1.529 s 10 runs
Summary
target/release/brrr ran
1.50 ± 0.03 times faster than target/release/brrr-org