embed: simplify the code

Use stringslite and bytealg to simplify the code and to remove redundent
helper functions.

Change-Id: I665a8313d9b91201b147b255290058f162cf0894
GitHub-Last-Rev: e9e3beb
GitHub-Pull-Request: #67515
Reviewed-on: https://go-review.googlesource.com/c/go/+/586715
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

src/embed/embed.go

@@ -130,6 +130,8 @@ package embed
 
 import (
 	"errors"
+	"internal/bytealg"
+	"internal/stringslite"
 	"io"
 	"io/fs"
 	"time"
@@ -185,29 +187,14 @@ type FS struct {
 // comment in the FS struct above. isDir reports whether the
 // final trailing slash was present, indicating that name is a directory.
 func split(name string) (dir, elem string, isDir bool) {
-	if name[len(name)-1] == '/' {
-		isDir = true
-		name = name[:len(name)-1]
-	}
-	i := len(name) - 1
-	for i >= 0 && name[i] != '/' {
-		i--
-	}
+	name, isDir = stringslite.CutSuffix(name, "/")
+	i := bytealg.LastIndexByteString(name, '/')
 	if i < 0 {
 		return ".", name, isDir
 	}
 	return name[:i], name[i+1:], isDir
 }
 
-// trimSlash trims a trailing slash from name, if present,
-// returning the possibly shortened name.
-func trimSlash(name string) string {
-	if len(name) > 0 && name[len(name)-1] == '/' {
-		return name[:len(name)-1]
-	}
-	return name
-}
-
 var (
 	_ fs.ReadDirFS  = FS{}
 	_ fs.ReadFileFS = FS{}
@@ -274,7 +261,7 @@ func (f FS) lookup(name string) *file {
 		idir, ielem, _ := split(files[i].name)
 		return idir > dir || idir == dir && ielem >= elem
 	})
-	if i < len(files) && trimSlash(files[i].name) == name {
+	if i < len(files) && stringslite.TrimSuffix(files[i].name, "/") == name {
 		return &files[i]
 	}
 	return nil