diff --git a/internal/cmd/generator/vm.go.tmpl b/internal/cmd/generator/vm.go.tmpl
index f45a593..70a45e4 100644
--- a/internal/cmd/generator/vm.go.tmpl
+++ b/internal/cmd/generator/vm.go.tmpl
@@ -403,11 +403,12 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			mapCtx := encoder.NewMapContext(mlen)
+			unorderedMap := (ctx.Option.Flag & encoder.UnorderedMapOption) != 0
+			mapCtx := encoder.NewMapContext(mlen, unorderedMap)
 			mapiterinit(code.Type, uptr, &mapCtx.Iter)
 			store(ctxptr, code.Idx, uintptr(unsafe.Pointer(mapCtx)))
 			ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
+			if unorderedMap {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
 				mapCtx.Start = len(b)
diff --git a/internal/encoder/decode_rune.go b/internal/encoder/decode_rune.go
index 1087f0b..35c959d 100644
--- a/internal/encoder/decode_rune.go
+++ b/internal/encoder/decode_rune.go
@@ -44,13 +44,6 @@ var first = [256]uint8{
 	s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
 }
 
-// acceptRange gives the range of valid values for the second byte in a UTF-8
-// sequence.
-type acceptRange struct {
-	lo uint8 // lowest value for second byte.
-	hi uint8 // highest value for second byte.
-}
-
 const (
 	lineSep      = byte(168) //'\u2028'
 	paragraphSep = byte(169) //'\u2029'
@@ -80,25 +73,31 @@ func decodeRuneInString(s string) (decodeRuneState, int) {
 		return validUTF8State, 1
 	}
 	sz := int(x & 7)
-	var accept acceptRange
-	switch x >> 4 {
-	case 0:
-		accept = acceptRange{locb, hicb}
-	case 1:
-		accept = acceptRange{0xA0, hicb}
-	case 2:
-		accept = acceptRange{locb, 0x9F}
-	case 3:
-		accept = acceptRange{0x90, hicb}
-	case 4:
-		accept = acceptRange{locb, 0x8F}
-	}
 	if n < sz {
 		return runeErrorState, 1
 	}
 	s1 := s[1]
-	if s1 < accept.lo || accept.hi < s1 {
-		return runeErrorState, 1
+	switch x >> 4 {
+	case 0:
+		if s1 < locb || hicb < s1 {
+			return runeErrorState, 1
+		}
+	case 1:
+		if s1 < 0xA0 || hicb < s1 {
+			return runeErrorState, 1
+		}
+	case 2:
+		if s1 < locb || 0x9F < s1 {
+			return runeErrorState, 1
+		}
+	case 3:
+		if s1 < 0x90 || hicb < s1 {
+			return runeErrorState, 1
+		}
+	case 4:
+		if s1 < locb || 0x8F < s1 {
+			return runeErrorState, 1
+		}
 	}
 	if sz <= 2 {
 		return validUTF8State, 2
diff --git a/internal/encoder/encoder.go b/internal/encoder/encoder.go
index 4ba3158..d210ec4 100644
--- a/internal/encoder/encoder.go
+++ b/internal/encoder/encoder.go
@@ -275,12 +275,14 @@ var mapContextPool = sync.Pool{
 	},
 }
 
-func NewMapContext(mapLen int) *MapContext {
+func NewMapContext(mapLen int, unorderedMap bool) *MapContext {
 	ctx := mapContextPool.Get().(*MapContext)
-	if len(ctx.Slice.Items) < mapLen {
-		ctx.Slice.Items = make([]MapItem, mapLen)
-	} else {
-		ctx.Slice.Items = ctx.Slice.Items[:mapLen]
+	if !unorderedMap {
+		if len(ctx.Slice.Items) < mapLen {
+			ctx.Slice.Items = make([]MapItem, mapLen)
+		} else {
+			ctx.Slice.Items = ctx.Slice.Items[:mapLen]
+		}
 	}
 	ctx.Buf = ctx.Buf[:0]
 	ctx.Iter = mapIter{}
diff --git a/internal/encoder/vm/vm.go b/internal/encoder/vm/vm.go
index f45a593..70a45e4 100644
--- a/internal/encoder/vm/vm.go
+++ b/internal/encoder/vm/vm.go
@@ -403,11 +403,12 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			mapCtx := encoder.NewMapContext(mlen)
+			unorderedMap := (ctx.Option.Flag & encoder.UnorderedMapOption) != 0
+			mapCtx := encoder.NewMapContext(mlen, unorderedMap)
 			mapiterinit(code.Type, uptr, &mapCtx.Iter)
 			store(ctxptr, code.Idx, uintptr(unsafe.Pointer(mapCtx)))
 			ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
+			if unorderedMap {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
 				mapCtx.Start = len(b)
diff --git a/internal/encoder/vm_color/vm.go b/internal/encoder/vm_color/vm.go
index 4a2e3c7..6461bb5 100644
--- a/internal/encoder/vm_color/vm.go
+++ b/internal/encoder/vm_color/vm.go
@@ -403,11 +403,12 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			mapCtx := encoder.NewMapContext(mlen)
+			unorderedMap := (ctx.Option.Flag & encoder.UnorderedMapOption) != 0
+			mapCtx := encoder.NewMapContext(mlen, unorderedMap)
 			mapiterinit(code.Type, uptr, &mapCtx.Iter)
 			store(ctxptr, code.Idx, uintptr(unsafe.Pointer(mapCtx)))
 			ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
+			if unorderedMap {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
 				mapCtx.Start = len(b)
diff --git a/internal/encoder/vm_color_indent/vm.go b/internal/encoder/vm_color_indent/vm.go
index a9fb725..c428fbe 100644
--- a/internal/encoder/vm_color_indent/vm.go
+++ b/internal/encoder/vm_color_indent/vm.go
@@ -403,11 +403,12 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			mapCtx := encoder.NewMapContext(mlen)
+			unorderedMap := (ctx.Option.Flag & encoder.UnorderedMapOption) != 0
+			mapCtx := encoder.NewMapContext(mlen, unorderedMap)
 			mapiterinit(code.Type, uptr, &mapCtx.Iter)
 			store(ctxptr, code.Idx, uintptr(unsafe.Pointer(mapCtx)))
 			ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
+			if unorderedMap {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
 				mapCtx.Start = len(b)
diff --git a/internal/encoder/vm_indent/vm.go b/internal/encoder/vm_indent/vm.go
index a023472..90ae850 100644
--- a/internal/encoder/vm_indent/vm.go
+++ b/internal/encoder/vm_indent/vm.go
@@ -403,11 +403,12 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			mapCtx := encoder.NewMapContext(mlen)
+			unorderedMap := (ctx.Option.Flag & encoder.UnorderedMapOption) != 0
+			mapCtx := encoder.NewMapContext(mlen, unorderedMap)
 			mapiterinit(code.Type, uptr, &mapCtx.Iter)
 			store(ctxptr, code.Idx, uintptr(unsafe.Pointer(mapCtx)))
 			ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
+			if unorderedMap {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
 				mapCtx.Start = len(b)