net/textproto: eliminate some bounds checks
This change lifts bounds checks out of loops in the trim function.
Here are some benchmark results (no change to allocations):
goos: darwin
goarch: amd64
pkg: net/textproto
cpu: Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
│ old │ new │
│ sec/op │ sec/op vs base │
ReadMIMEHeader/client_headers-8 3.531µ ± 3% 3.506µ ± 1% ~ (p=0.068 n=20)
ReadMIMEHeader/server_headers-8 2.409µ ± 0% 2.384µ ± 1% -1.02% (p=0.000 n=20)
Uncommon-8 545.2n ± 1% 536.7n ± 0% -1.58% (p=0.000 n=20)
geomean 1.667µ 1.649µ -1.10%
Change-Id: Ia6d4ac516497fd3521122ce9b97173a285b61e12
GitHub-Last-Rev:
580f35afceda1993da70a023ce5c28280bda1ff6
GitHub-Pull-Request: golang/go#75126
Reviewed-on: https://go-review.googlesource.com/c/go/+/698715
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>