This is a quick test on the best way to find the string length of an itoa output.

Our base line is ItoalenWithItoa, e.g. len(strconv.Itoa(123)). This is the worst we can do: not only is performance O(n), there is also allocation per call.

Using log (ItoalenWithLog) is a lot better. At least we're getting O(1).

Repeated multiplication (ItoalenWithMul) beats using log, although we're back to being O(n). I tried using bit shift (ItoalenWithMul2), with exactly the same performance. Looks like Go compiler has optimized this away already.

The fastest algo I found that is still elegant is division by 2 (ItoalenWithDiv2). It's basically O(1), or at least a very gradual O(n) slope. It's also faster than all the above.

The actual winner is, unsurprisingly, just old plain if...else branching. It's ugly but...yeah it works.

Create log:

GO111MODULE=off go test -v -bench=. > bench_result.log

Massage into csv, then paste into Excel:

Get-Clipboard | where { $_ -like "*-2*" } | % { 
    $funcName = $_.Split(' ')[0].Split('/')[0].Substring('BenchmarkItoalenWith'.Length)
    $intlen = $_.Split(' ')[0].Split('/')[1].Substring('intlen_'.Length).Split('-')[0]
    $speed =  $_.Substring($_.LastIndexOf('  ')).Trim().Split(' ')[0]

    '{0},{1},{2}' -f $funcName, $intlen, $speed
}