3 files changed, 5 insertions, 21 deletions
diff --git a/src/strings/iter.go b/src/strings/iter.go
index 69fe031739..84e763a834 100644
--- a/src/strings/iter.go
+++ b/src/strings/iter.go
@@ -117,11 +117,7 @@ func FieldsFuncSeq(s string, f func(rune) bool) iter.Seq[string] {
 	return func(yield func(string) bool) {
 		start := -1
 		for i := 0; i < len(s); {
-			size := 1
-			r := rune(s[i])
-			if r >= utf8.RuneSelf {
-				r, size = utf8.DecodeRuneInString(s[i:])
-			}
+			r, size := utf8.DecodeRuneInString(s[i:])
 			if f(r) {
 				if start >= 0 {
 					if !yield(s[start:i]) {
diff --git a/src/strings/reader.go b/src/strings/reader.go
index 497ffb7a39..f12c9b18b3 100644
--- a/src/strings/reader.go
+++ b/src/strings/reader.go
@@ -90,10 +90,6 @@ func (r *Reader) ReadRune() (ch rune, size int, err error) {
 		return 0, 0, io.EOF
 	}
 	r.prevRune = int(r.i)
-	if c := r.s[r.i]; c < utf8.RuneSelf {
-		r.i++
-		return rune(c), 1, nil
-	}
 	ch, size = utf8.DecodeRuneInString(r.s[r.i:])
 	r.i += int64(size)
 	return
diff --git a/src/strings/strings.go b/src/strings/strings.go
index 74007977d9..3cc3e79f98 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -896,7 +896,7 @@ func TrimLeftFunc(s string, f func(rune) bool) string {
 // Unicode code points c satisfying f(c) removed.
 func TrimRightFunc(s string, f func(rune) bool) string {
 	i := lastIndexFunc(s, f, false)
-	if i >= 0 && s[i] >= utf8.RuneSelf {
+	if i >= 0 {
 		_, wid := utf8.DecodeRuneInString(s[i:])
 		i += wid
 	} else {
@@ -1028,10 +1028,7 @@ func trimLeftASCII(s string, as *asciiSet) string {
 
 func trimLeftUnicode(s, cutset string) string {
 	for len(s) > 0 {
-		r, n := rune(s[0]), 1
-		if r >= utf8.RuneSelf {
-			r, n = utf8.DecodeRuneInString(s)
-		}
+		r, n := utf8.DecodeRuneInString(s)
 		if !ContainsRune(cutset, r) {
 			break
 		}
@@ -1224,13 +1221,8 @@ hasUnicode:
 		}
 
 		// Extract first rune from second string.
-		var tr rune
-		if t[0] < utf8.RuneSelf {
-			tr, t = rune(t[0]), t[1:]
-		} else {
-			r, size := utf8.DecodeRuneInString(t)
-			tr, t = r, t[size:]
-		}
+		tr, size := utf8.DecodeRuneInString(t)
+		t = t[size:]
 
 		// If they match, keep going; if not, return false.