Decode: use unsafe []byte->string conversion for discarded value

[odeke-em]

For Decode's MLI4I, we invoke strconv.Atoi after string(*b)
which incurs a []byte->string allocation. The converted []byte->string
is discarded so anyways it is okay to use unsafe, as the string is
never used again. You can see the results at https://dashboard.github.orijtech.com/benchmark/dbb0fca65f644d95bcf8d0c8caafc601

Results:

• time/op (ns/op)
  Encoding/Decoding_2I-8 7.5ns ± 1% 6.7ns ± 0% -10.36% (p=0.000 n=10+9)
  Encoding/Decoding_4E-8 8.8ns ± 0% 7.9ns ± 0% -10.35% (p=0.000 n=10+10)
  Encoding/Decoding_A4E-8 38ns ± 1% 17ns ± 0% -54.84% (p=0.000 n=10+10)

• allocs/op (B/op)
  Encoding/Decoding_A4E-8 4.0B ± 0% 0 -100.00% (p=0.000 n=10+10)

• allocs/op (N/op)
  Encoding/Decoding_A4E-8 1.0 ± 0% 0 -100.00% (p=0.000 n=10+10)

Or visually

Problem Statement

What is the current behavior? Why and how does it need to change?

string(*b) incurs a []byte->string allocation yet the value will be discarded.

Description of Change

Please include a summary of the change and, if applicable, tag related issues, add code snippets or logs.

This change removes a []byte->string allocation

Breaking Change

Is this a breaking change?

No.

Caveats

Please list any caveats or special considerations for this change.

It uses unsafe, but the usage is isolated as we directly insert the converted string into strconv.Atoi, so this isn't a caveat really. /cc @kirbyquerby @cuonglm @madflojo

[madflojo]

@odeke-em thanks for opening this, sorry for the delay in comments. The change looks pretty clear and I see what you mean on the use of unsafe being pretty isolated.

I’ve not explored unsafe very much so let me do a bit of research on any downsides of using unsafe.

Thanks again for opening this.

[odeke-em]

@odeke-em thanks for opening this, sorry for the delay in comments. The change looks pretty clear and I see what you mean on the use of unsafe being pretty isolated.

I’ve not explored unsafe very much so let me do a bit of research on any downsides of using unsafe.

Thanks again for opening this.

No rush at all @madflojo, please take your time! I put it up so you can indeed explore trade-offs and benefits.

[madflojo]

After going through it, I think I'm good with this change. Thanks @odeke-em!