mime: reduce allocs incurred by ParseMediaType
This change is mostly gardening. It simplifies ParseMediaType and its
helper functions and reduces the amount of allocations they incur.
Here are some benchmark results:
goos: darwin
goarch: amd64
pkg: mime
cpu: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
│ old │ new │
│ sec/op │ sec/op vs base │
ParseMediaType-8 55.26µ ± 1% 54.54µ ± 1% -1.30% (p=0.000 n=20)
ParseMediaTypeBogus-8 3.551µ ± 0% 3.427µ ± 0% -3.48% (p=0.000 n=20)
geomean 14.01µ 13.67µ -2.39%
│ old │ new │
│ B/op │ B/op vs base │
ParseMediaType-8 38.48Ki ± 0% 37.38Ki ± 0% -2.85% (p=0.000 n=20)
ParseMediaTypeBogus-8 2.531Ki ± 0% 2.469Ki ± 0% -2.47% (p=0.000 n=20)
geomean 9.869Ki 9.606Ki -2.66%
│ old │ new │
│ allocs/op │ allocs/op vs base │
ParseMediaType-8 457.0 ± 0% 425.0 ± 0% -7.00% (p=0.000 n=20)
ParseMediaTypeBogus-8 25.00 ± 0% 21.00 ± 0% -16.00% (p=0.000 n=20)
geomean 106.9 94.47 -11.62%
Change-Id: I51198b40396afa51531794a57c50aa88975eae1d
GitHub-Last-Rev:
c44e2a2577386d1d776498d29e31821326e20b92
GitHub-Pull-Request: golang/go#75565
Reviewed-on: https://go-review.googlesource.com/c/go/+/705715
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Emmanuel Odeke <emmanuel@orijtech.com>