Avoid string allocation to get length of port

[qsantos]

Following #817 (review), it was raise that port.to_string().len() could be optimized to avoid allocating a string.

[qsantos]

Ah, the CI is targeting 1.51.0 but checked_ilog10 is from 1.67.0. Did you have something else in mind @klensy?

[codecov]

Codecov Report

Patch coverage: 87.50% and no project coverage change

Comparison is base (74b8694) 82.73% compared to head (28c2d6c) 82.73%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #823   +/-   ##
=======================================
  Coverage   82.73%   82.73%           
=======================================
  Files          20       20           
  Lines        3330     3337    +7     
=======================================
+ Hits         2755     2761    +6     
- Misses        575      576    +1     

Impacted Files	Coverage Δ
url/src/slicing.rs	91.30% <87.50%> (-0.64%)	⬇️

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[klensy]

It can be something like https://stackoverflow.com/a/69298721 where you simply multiply by 10 and compare.

[qsantos]

I have made it a fallback with some tests for edge cases. What do you think?

[valenting]

How about a simple match statement? https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=b2fffe2e3cc3683b55cf4d0e0789795b

fn count_digits(n: u16) -> u8 {
    match n {
        0..=9 => 1,
        10..=99 => 2,
        100..=999 => 3,
        1000..=9999 => 4,
        10000..=65535 => 5,
    }
}

[qsantos]

They compile to the same binary! In fact, even for u32 or u64, the compiler just unrolls the loop. It does use a trick for u64 because there are no CMP instructions with an immediate 64 bit value on x86_64 (if I understand correctly).

In any case, your version looks much nicer, and it is much easier to convince oneself that it is correct, so I have pushed it.

[valenting]

Thank you! 🙏