diff --git a/internal/encoder/decode_rune.go b/internal/encoder/decode_rune.go
index 5c8de16..1fa1074 100644
--- a/internal/encoder/decode_rune.go
+++ b/internal/encoder/decode_rune.go
@@ -2,22 +2,7 @@ package encoder
 
 import "unicode/utf8"
 
-// Code points in the surrogate range are not valid for UTF-8.
 const (
-	surrogateMin = 0xD800
-	surrogateMax = 0xDFFF
-)
-
-const (
-	maskx = 63 //0b00111111
-	mask2 = 31 //0b00011111
-	mask3 = 15 //0b00001111
-	mask4 = 7  //0b00000111
-
-	rune1Max = 1<<7 - 1
-	rune2Max = 1<<11 - 1
-	rune3Max = 1<<16 - 1
-
 	// The default lowest and highest continuation byte.
 	locb = 128 //0b10000000
 	hicb = 191 //0b10111111
diff --git a/internal/encoder/string.go b/internal/encoder/string.go
index 2d7e363..236e2e9 100644
--- a/internal/encoder/string.go
+++ b/internal/encoder/string.go
@@ -348,53 +348,6 @@ var needEscape = [256]bool{
 
 var hex = "0123456789abcdef"
 
-// escapeIndex finds the index of the first char in `s` that requires escaping.
-// A char requires escaping if it's outside of the range of [0x20, 0x7F] or if
-// it includes a double quote or backslash.
-// If no chars in `s` require escaping, the return value is -1.
-func escapeIndex(s string) int {
-	chunks := stringToUint64Slice(s)
-	for _, n := range chunks {
-		// combine masks before checking for the MSB of each byte. We include
-		// `n` in the mask to check whether any of the *input* byte MSBs were
-		// set (i.e. the byte was outside the ASCII range).
-		mask := n | below(n, 0x20) | contains(n, '"') | contains(n, '\\')
-		if (mask & msb) != 0 {
-			return bits.TrailingZeros64(mask&msb) / 8
-		}
-	}
-
-	valLen := len(s)
-	for i := len(chunks) * 8; i < valLen; i++ {
-		if needEscape[s[i]] {
-			return i
-		}
-	}
-
-	return -1
-}
-
-// below return a mask that can be used to determine if any of the bytes
-// in `n` are below `b`. If a byte's MSB is set in the mask then that byte was
-// below `b`. The result is only valid if `b`, and each byte in `n`, is below
-// 0x80.
-func below(n uint64, b byte) uint64 {
-	return n - expand(b)
-}
-
-// contains returns a mask that can be used to determine if any of the
-// bytes in `n` are equal to `b`. If a byte's MSB is set in the mask then
-// that byte is equal to `b`. The result is only valid if `b`, and each
-// byte in `n`, is below 0x80.
-func contains(n uint64, b byte) uint64 {
-	return (n ^ expand(b)) - lsb
-}
-
-// expand puts the specified byte into each of the 8 bytes of a uint64.
-func expand(b byte) uint64 {
-	return lsb * uint64(b)
-}
-
 //nolint:govet
 func stringToUint64Slice(s string) []uint64 {
 	return *(*[]uint64)(unsafe.Pointer(&reflect.SliceHeader{
@@ -539,19 +492,37 @@ func appendString(buf []byte, s string) []byte {
 		return append(buf, `""`...)
 	}
 	buf = append(buf, '"')
-	var escapeIdx int
+	var (
+		i, j int
+	)
 	if valLen >= 8 {
-		if escapeIdx = escapeIndex(s); escapeIdx < 0 {
-			return append(append(buf, s...), '"')
+		chunks := stringToUint64Slice(s)
+		for _, n := range chunks {
+			// combine masks before checking for the MSB of each byte. We include
+			// `n` in the mask to check whether any of the *input* byte MSBs were
+			// set (i.e. the byte was outside the ASCII range).
+			mask := n | (n - (lsb * 0x20)) |
+				((n ^ (lsb * '"')) - lsb) |
+				((n ^ (lsb * '\\')) - lsb)
+			if (mask & msb) != 0 {
+				j = bits.TrailingZeros64(mask&msb) / 8
+				goto ESCAPE_END
+			}
 		}
+		valLen := len(s)
+		for i := len(chunks) * 8; i < valLen; i++ {
+			if needEscape[s[i]] {
+				j = i
+				goto ESCAPE_END
+			}
+		}
+		return append(append(buf, s...), '"')
 	}
-
-	i := 0
-	j := escapeIdx
+ESCAPE_END:
 	for j < valLen {
 		c := s[j]
 
-		if c >= 0x20 && c <= 0x7f && c != '\\' && c != '"' {
+		if !needEscape[c] {
 			// fast path: most of the time, printable ascii characters are used
 			j++
 			continue