diff --git a/internal/go-json/cmd/generator/vm.go.tmpl b/internal/go-json/cmd/generator/vm.go.tmpl
index 5d3b95713d..6c8292d01c 100644
--- a/internal/go-json/cmd/generator/vm.go.tmpl
+++ b/internal/go-json/cmd/generator/vm.go.tmpl
@@ -403,48 +403,41 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			iter := mapiterinit(code.Type, uptr)
-			ctx.KeepRefs = append(ctx.KeepRefs, iter)
-			store(ctxptr, code.ElemIdx, 0)
-			store(ctxptr, code.Length, uintptr(mlen))
-			store(ctxptr, code.MapIter, uintptr(iter))
+			mapCtx := encoder.NewMapContext(mlen)
+			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 {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
-				mapCtx := encoder.NewMapContext(mlen)
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-				store(ctxptr, code.End.MapPos, uintptr(unsafe.Pointer(mapCtx)))
+				mapCtx.Start = len(b)
+				mapCtx.First = len(b)
 			}
-			key := mapiterkey(iter)
+			key := mapiterkey(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(key))
 			code = code.Next
 		case encoder.OpMapKey:
-			idx := load(ctxptr, code.ElemIdx)
-			length := load(ctxptr, code.Length)
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
+			idx := mapCtx.Idx
 			idx++
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
-				if idx < length {
+				if idx < mapCtx.Len {
 					b = appendMapKeyIndent(ctx, code, b)
-					store(ctxptr, code.ElemIdx, idx)
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					key := mapiterkey(iter)
+					mapCtx.Idx = int(idx)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
 					b = appendObjectEnd(ctx, code, b)
+					encoder.ReleaseMapContext(mapCtx)
 					code = code.End.Next
 				}
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				if idx < length {
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					store(ctxptr, code.ElemIdx, idx)
-					key := mapiterkey(iter)
+				mapCtx.Slice.Items[mapCtx.Idx].Value = b[mapCtx.Start:len(b)]
+				if idx < mapCtx.Len {
+					mapCtx.Idx = int(idx)
+					mapCtx.Start = len(b)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
@@ -452,46 +445,27 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				}
 			}
 		case encoder.OpMapValue:
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
 				b = appendColon(ctx, b)
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
+				mapCtx.Slice.Items[mapCtx.Idx].Key = b[mapCtx.Start:len(b)]
+				mapCtx.Start = len(b)
 			}
-			ptr := load(ctxptr, code.MapIter)
-			iter := ptrToUnsafePtr(ptr)
-			value := mapitervalue(iter)
+			value := mapitervalue(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(value))
-			mapiternext(iter)
+			mapiternext(&mapCtx.Iter)
 			code = code.Next
 		case encoder.OpMapEnd:
 			// this operation only used by sorted map.
-			length := int(load(ctxptr, code.Length))
-			ptr := load(ctxptr, code.MapPos)
-			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-			pos := mapCtx.Pos
-			for i := 0; i < length; i++ {
-				startKey := pos[i*2]
-				startValue := pos[i*2+1]
-				var endValue int
-				if i+1 < length {
-					endValue = pos[i*2+2]
-				} else {
-					endValue = len(b)
-				}
-				mapCtx.Slice.Items = append(mapCtx.Slice.Items, encoder.MapItem{
-					Key:   b[startKey:startValue],
-					Value: b[startValue:endValue],
-				})
-			}
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			sort.Sort(mapCtx.Slice)
 			buf := mapCtx.Buf
 			for _, item := range mapCtx.Slice.Items {
 				buf = appendMapKeyValue(ctx, code, buf, item.Key, item.Value)
 			}
 			buf = appendMapEnd(ctx, code, buf)
-			b = b[:pos[0]]
+			b = b[:mapCtx.First]
 			b = append(b, buf...)
 			mapCtx.Buf = buf
 			encoder.ReleaseMapContext(mapCtx)
diff --git a/internal/go-json/encoder/decode_rune.go b/internal/go-json/encoder/decode_rune.go
new file mode 100644
index 0000000000..1087f0b616
--- /dev/null
+++ b/internal/go-json/encoder/decode_rune.go
@@ -0,0 +1,127 @@
+package encoder
+
+import "unicode/utf8"
+
+const (
+	// The default lowest and highest continuation byte.
+	locb = 128 //0b10000000
+	hicb = 191 //0b10111111
+
+	// These names of these constants are chosen to give nice alignment in the
+	// table below. The first nibble is an index into acceptRanges or F for
+	// special one-byte cases. The second nibble is the Rune length or the
+	// Status for the special one-byte case.
+	xx = 0xF1 // invalid: size 1
+	as = 0xF0 // ASCII: size 1
+	s1 = 0x02 // accept 0, size 2
+	s2 = 0x13 // accept 1, size 3
+	s3 = 0x03 // accept 0, size 3
+	s4 = 0x23 // accept 2, size 3
+	s5 = 0x34 // accept 3, size 4
+	s6 = 0x04 // accept 0, size 4
+	s7 = 0x44 // accept 4, size 4
+)
+
+// first is information about the first byte in a UTF-8 sequence.
+var first = [256]uint8{
+	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
+	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
+	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
+	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
+	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
+	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
+	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
+	xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
+	s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
+	s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
+	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'
+)
+
+type decodeRuneState int
+
+const (
+	validUTF8State decodeRuneState = iota
+	runeErrorState
+	lineSepState
+	paragraphSepState
+)
+
+func decodeRuneInString(s string) (decodeRuneState, int) {
+	n := len(s)
+	s0 := s[0]
+	x := first[s0]
+	if x >= as {
+		// The following code simulates an additional check for x == xx and
+		// handling the ASCII and invalid cases accordingly. This mask-and-or
+		// approach prevents an additional branch.
+		mask := rune(x) << 31 >> 31 // Create 0x0000 or 0xFFFF.
+		if rune(s[0])&^mask|utf8.RuneError&mask == utf8.RuneError {
+			return runeErrorState, 1
+		}
+		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
+	}
+	if sz <= 2 {
+		return validUTF8State, 2
+	}
+	s2 := s[2]
+	if s2 < locb || hicb < s2 {
+		return runeErrorState, 1
+	}
+	if sz <= 3 {
+		// separator character prefixes: [2]byte{226, 128}
+		if s0 == 226 && s1 == 128 {
+			switch s2 {
+			case lineSep:
+				return lineSepState, 3
+			case paragraphSep:
+				return paragraphSepState, 3
+			}
+		}
+		return validUTF8State, 3
+	}
+	s3 := s[3]
+	if s3 < locb || hicb < s3 {
+		return runeErrorState, 1
+	}
+	return validUTF8State, 4
+}
diff --git a/internal/go-json/encoder/encoder.go b/internal/go-json/encoder/encoder.go
index f21ec1d4d8..f4d23ebb73 100644
--- a/internal/go-json/encoder/encoder.go
+++ b/internal/go-json/encoder/encoder.go
@@ -222,33 +222,54 @@ func (m *Mapslice) Swap(i, j int) {
 	m.Items[i], m.Items[j] = m.Items[j], m.Items[i]
 }
 
+//nolint:structcheck,unused
+type mapIter struct {
+	key         unsafe.Pointer
+	elem        unsafe.Pointer
+	t           unsafe.Pointer
+	h           unsafe.Pointer
+	buckets     unsafe.Pointer
+	bptr        unsafe.Pointer
+	overflow    unsafe.Pointer
+	oldoverflow unsafe.Pointer
+	startBucket uintptr
+	offset      uint8
+	wrapped     bool
+	B           uint8
+	i           uint8
+	bucket      uintptr
+	checkBucket uintptr
+}
+
 type MapContext struct {
-	Pos   []int
+	Start int
+	First int
+	Idx   int
 	Slice *Mapslice
 	Buf   []byte
+	Len   int
+	Iter  mapIter
 }
 
 var mapContextPool = sync.Pool{
 	New: func() interface{} {
-		return &MapContext{}
+		return &MapContext{
+			Slice: &Mapslice{},
+		}
 	},
 }
 
 func NewMapContext(mapLen int) *MapContext {
 	ctx := mapContextPool.Get().(*MapContext)
-	if ctx.Slice == nil {
-		ctx.Slice = &Mapslice{
-			Items: make([]MapItem, 0, mapLen),
-		}
-	}
-	if cap(ctx.Pos) < (mapLen*2 + 1) {
-		ctx.Pos = make([]int, 0, mapLen*2+1)
-		ctx.Slice.Items = make([]MapItem, 0, mapLen)
+	if len(ctx.Slice.Items) < mapLen {
+		ctx.Slice.Items = make([]MapItem, mapLen)
 	} else {
-		ctx.Pos = ctx.Pos[:0]
-		ctx.Slice.Items = ctx.Slice.Items[:0]
+		ctx.Slice.Items = ctx.Slice.Items[:mapLen]
 	}
 	ctx.Buf = ctx.Buf[:0]
+	ctx.Iter = mapIter{}
+	ctx.Idx = 0
+	ctx.Len = mapLen
 	return ctx
 }
 
@@ -256,17 +277,17 @@ func ReleaseMapContext(c *MapContext) {
 	mapContextPool.Put(c)
 }
 
-//go:linkname MapIterInit reflect.mapiterinit
+//go:linkname MapIterInit runtime.mapiterinit
 //go:noescape
-func MapIterInit(mapType *runtime.Type, m unsafe.Pointer) unsafe.Pointer
+func MapIterInit(mapType *runtime.Type, m unsafe.Pointer, it *mapIter)
 
 //go:linkname MapIterKey reflect.mapiterkey
 //go:noescape
-func MapIterKey(it unsafe.Pointer) unsafe.Pointer
+func MapIterKey(it *mapIter) unsafe.Pointer
 
 //go:linkname MapIterNext reflect.mapiternext
 //go:noescape
-func MapIterNext(it unsafe.Pointer)
+func MapIterNext(it *mapIter)
 
 //go:linkname MapLen reflect.maplen
 //go:noescape
diff --git a/internal/go-json/encoder/map112.go b/internal/go-json/encoder/map112.go
index 31858d0001..e96ffadf7a 100644
--- a/internal/go-json/encoder/map112.go
+++ b/internal/go-json/encoder/map112.go
@@ -1,3 +1,4 @@
+//go:build !go1.13
 // +build !go1.13
 
 package encoder
@@ -5,4 +6,4 @@ package encoder
 import "unsafe"
 
 //go:linkname MapIterValue reflect.mapitervalue
-func MapIterValue(it unsafe.Pointer) unsafe.Pointer
+func MapIterValue(it *mapIter) unsafe.Pointer
diff --git a/internal/go-json/encoder/map113.go b/internal/go-json/encoder/map113.go
index f49c27bedb..9b69dcc360 100644
--- a/internal/go-json/encoder/map113.go
+++ b/internal/go-json/encoder/map113.go
@@ -1,3 +1,4 @@
+//go:build go1.13
 // +build go1.13
 
 package encoder
@@ -5,4 +6,4 @@ package encoder
 import "unsafe"
 
 //go:linkname MapIterValue reflect.mapiterelem
-func MapIterValue(it unsafe.Pointer) unsafe.Pointer
+func MapIterValue(it *mapIter) unsafe.Pointer
diff --git a/internal/go-json/encoder/opcode.go b/internal/go-json/encoder/opcode.go
index e61dff4b0f..8b8c8b0678 100644
--- a/internal/go-json/encoder/opcode.go
+++ b/internal/go-json/encoder/opcode.go
@@ -39,10 +39,8 @@ type Opcode struct {
 
 	Type       *runtime.Type // go type
 	Jmp        *CompiledCode // for recursive call
-	ElemIdx    uint32        // offset to access array/slice/map elem
-	Length     uint32        // offset to access slice/map length or array length
-	MapIter    uint32        // offset to access map iterator
-	MapPos     uint32        // offset to access position list for sorted map
+	ElemIdx    uint32        // offset to access array/slice elem
+	Length     uint32        // offset to access slice length or array length
 	Indent     uint32        // indent number
 	Size       uint32        // array/slice elem size
 	DisplayIdx uint32        // opcode index
@@ -91,8 +89,6 @@ func (c *Opcode) MaxIdx() uint32 {
 		c.Idx,
 		c.ElemIdx,
 		c.Length,
-		c.MapIter,
-		c.MapPos,
 		c.Size,
 	} {
 		if max < value {
@@ -341,8 +337,6 @@ func copyOpcode(code *Opcode) *Opcode {
 			DisplayKey: c.DisplayKey,
 			ElemIdx:    c.ElemIdx,
 			Length:     c.Length,
-			MapIter:    c.MapIter,
-			MapPos:     c.MapPos,
 			Size:       c.Size,
 			Indent:     c.Indent,
 			Jmp:        c.Jmp,
@@ -448,26 +442,21 @@ func (c *Opcode) dumpHead(code *Opcode) string {
 
 func (c *Opcode) dumpMapHead(code *Opcode) string {
 	return fmt.Sprintf(
-		`[%03d]%s%s ([idx:%d][elemIdx:%d][length:%d][mapIter:%d])`,
+		`[%03d]%s%s ([idx:%d])`,
 		code.DisplayIdx,
 		strings.Repeat("-", int(code.Indent)),
 		code.Op,
 		code.Idx/uintptrSize,
-		code.ElemIdx/uintptrSize,
-		code.Length/uintptrSize,
-		code.MapIter/uintptrSize,
 	)
 }
 
 func (c *Opcode) dumpMapEnd(code *Opcode) string {
 	return fmt.Sprintf(
-		`[%03d]%s%s ([idx:%d][mapPos:%d][length:%d])`,
+		`[%03d]%s%s ([idx:%d])`,
 		code.DisplayIdx,
 		strings.Repeat("-", int(code.Indent)),
 		code.Op,
 		code.Idx/uintptrSize,
-		code.MapPos/uintptrSize,
-		code.Length/uintptrSize,
 	)
 }
 
@@ -504,25 +493,21 @@ func (c *Opcode) dumpField(code *Opcode) string {
 
 func (c *Opcode) dumpKey(code *Opcode) string {
 	return fmt.Sprintf(
-		`[%03d]%s%s ([idx:%d][elemIdx:%d][length:%d][mapIter:%d])`,
+		`[%03d]%s%s ([idx:%d])`,
 		code.DisplayIdx,
 		strings.Repeat("-", int(code.Indent)),
 		code.Op,
 		code.Idx/uintptrSize,
-		code.ElemIdx/uintptrSize,
-		code.Length/uintptrSize,
-		code.MapIter/uintptrSize,
 	)
 }
 
 func (c *Opcode) dumpValue(code *Opcode) string {
 	return fmt.Sprintf(
-		`[%03d]%s%s ([idx:%d][mapIter:%d])`,
+		`[%03d]%s%s ([idx:%d])`,
 		code.DisplayIdx,
 		strings.Repeat("-", int(code.Indent)),
 		code.Op,
 		code.Idx/uintptrSize,
-		code.MapIter/uintptrSize,
 	)
 }
 
@@ -629,19 +614,11 @@ func newArrayElemCode(ctx *compileContext, typ *runtime.Type, head *Opcode, leng
 func newMapHeaderCode(ctx *compileContext, typ *runtime.Type) *Opcode {
 	idx := opcodeOffset(ctx.ptrIndex)
 	ctx.incPtrIndex()
-	elemIdx := opcodeOffset(ctx.ptrIndex)
-	ctx.incPtrIndex()
-	length := opcodeOffset(ctx.ptrIndex)
-	ctx.incPtrIndex()
-	mapIter := opcodeOffset(ctx.ptrIndex)
 	return &Opcode{
 		Op:         OpMap,
 		Type:       typ,
 		Idx:        idx,
 		DisplayIdx: ctx.opcodeIndex,
-		ElemIdx:    elemIdx,
-		Length:     length,
-		MapIter:    mapIter,
 		Indent:     ctx.indent,
 	}
 }
@@ -650,11 +627,8 @@ func newMapKeyCode(ctx *compileContext, typ *runtime.Type, head *Opcode) *Opcode
 	return &Opcode{
 		Op:         OpMapKey,
 		Type:       typ,
-		Idx:        opcodeOffset(ctx.ptrIndex),
+		Idx:        head.Idx,
 		DisplayIdx: ctx.opcodeIndex,
-		ElemIdx:    head.ElemIdx,
-		Length:     head.Length,
-		MapIter:    head.MapIter,
 		Indent:     ctx.indent,
 	}
 }
@@ -663,28 +637,20 @@ func newMapValueCode(ctx *compileContext, typ *runtime.Type, head *Opcode) *Opco
 	return &Opcode{
 		Op:         OpMapValue,
 		Type:       typ,
-		Idx:        opcodeOffset(ctx.ptrIndex),
+		Idx:        head.Idx,
 		DisplayIdx: ctx.opcodeIndex,
-		ElemIdx:    head.ElemIdx,
-		Length:     head.Length,
-		MapIter:    head.MapIter,
 		Indent:     ctx.indent,
 	}
 }
 
 func newMapEndCode(ctx *compileContext, typ *runtime.Type, head *Opcode) *Opcode {
-	mapPos := opcodeOffset(ctx.ptrIndex)
-	ctx.incPtrIndex()
-	idx := opcodeOffset(ctx.ptrIndex)
 	return &Opcode{
 		Op:         OpMapEnd,
 		Type:       typ,
-		Idx:        idx,
-		Next:       newEndOp(ctx, typ),
+		Idx:        head.Idx,
 		DisplayIdx: ctx.opcodeIndex,
-		Length:     head.Length,
-		MapPos:     mapPos,
 		Indent:     ctx.indent,
+		Next:       newEndOp(ctx, typ),
 	}
 }
 
diff --git a/internal/go-json/encoder/string.go b/internal/go-json/encoder/string.go
index a699dba19c..236e2e9927 100644
--- a/internal/go-json/encoder/string.go
+++ b/internal/go-json/encoder/string.go
@@ -3,7 +3,6 @@ package encoder
 import (
 	"math/bits"
 	"reflect"
-	"unicode/utf8"
 	"unsafe"
 )
 
@@ -349,53 +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{
@@ -489,10 +441,9 @@ ESCAPE_END:
 			i = j + 1
 			j = j + 1
 			continue
-		}
 
-		// This encodes bytes < 0x20 except for \t, \n and \r.
-		if c < 0x20 {
+		case 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0B, 0x0C, 0x0E, 0x0F, // 0x00-0x0F
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F: // 0x10-0x1F
 			buf = append(buf, s[i:j]...)
 			buf = append(buf, `\u00`...)
 			buf = append(buf, hex[c>>4], hex[c&0xF])
@@ -501,18 +452,14 @@ ESCAPE_END:
 			continue
 		}
 
-		r, size := utf8.DecodeRuneInString(s[j:])
-
-		if r == utf8.RuneError && size == 1 {
+		state, size := decodeRuneInString(s[j:])
+		switch state {
+		case runeErrorState:
 			buf = append(buf, s[i:j]...)
 			buf = append(buf, `\ufffd`...)
-			i = j + size
-			j = j + size
+			i = j + 1
+			j = j + 1
 			continue
-		}
-
-		switch r {
-		case '\u2028', '\u2029':
 			// U+2028 is LINE SEPARATOR.
 			// U+2029 is PARAGRAPH SEPARATOR.
 			// They are both technically valid characters in JSON strings,
@@ -520,14 +467,19 @@ ESCAPE_END:
 			// and can lead to security holes there. It is valid JSON to
 			// escape them, so we do so unconditionally.
 			// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
+		case lineSepState:
 			buf = append(buf, s[i:j]...)
-			buf = append(buf, `\u202`...)
-			buf = append(buf, hex[r&0xF])
-			i = j + size
-			j = j + size
+			buf = append(buf, `\u2028`...)
+			i = j + 3
+			j = j + 3
+			continue
+		case paragraphSepState:
+			buf = append(buf, s[i:j]...)
+			buf = append(buf, `\u2029`...)
+			i = j + 3
+			j = j + 3
 			continue
 		}
-
 		j += size
 	}
 
@@ -540,19 +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
@@ -594,10 +564,9 @@ func appendString(buf []byte, s string) []byte {
 			i = j + 1
 			j = j + 1
 			continue
-		}
 
-		// This encodes bytes < 0x20 except for \t, \n and \r.
-		if c < 0x20 {
+		case 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x0B, 0x0C, 0x0E, 0x0F, // 0x00-0x0F
+			0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F: // 0x10-0x1F
 			buf = append(buf, s[i:j]...)
 			buf = append(buf, `\u00`...)
 			buf = append(buf, hex[c>>4], hex[c&0xF])
@@ -606,18 +575,14 @@ func appendString(buf []byte, s string) []byte {
 			continue
 		}
 
-		r, size := utf8.DecodeRuneInString(s[j:])
-
-		if r == utf8.RuneError && size == 1 {
+		state, size := decodeRuneInString(s[j:])
+		switch state {
+		case runeErrorState:
 			buf = append(buf, s[i:j]...)
 			buf = append(buf, `\ufffd`...)
-			i = j + size
-			j = j + size
+			i = j + 1
+			j = j + 1
 			continue
-		}
-
-		switch r {
-		case '\u2028', '\u2029':
 			// U+2028 is LINE SEPARATOR.
 			// U+2029 is PARAGRAPH SEPARATOR.
 			// They are both technically valid characters in JSON strings,
@@ -625,14 +590,19 @@ func appendString(buf []byte, s string) []byte {
 			// and can lead to security holes there. It is valid JSON to
 			// escape them, so we do so unconditionally.
 			// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
+		case lineSepState:
 			buf = append(buf, s[i:j]...)
-			buf = append(buf, `\u202`...)
-			buf = append(buf, hex[r&0xF])
-			i = j + size
-			j = j + size
+			buf = append(buf, `\u2028`...)
+			i = j + 3
+			j = j + 3
+			continue
+		case paragraphSepState:
+			buf = append(buf, s[i:j]...)
+			buf = append(buf, `\u2029`...)
+			i = j + 3
+			j = j + 3
 			continue
 		}
-
 		j += size
 	}
 
diff --git a/internal/go-json/encoder/vm/vm.go b/internal/go-json/encoder/vm/vm.go
index 5d3b95713d..6c8292d01c 100644
--- a/internal/go-json/encoder/vm/vm.go
+++ b/internal/go-json/encoder/vm/vm.go
@@ -403,48 +403,41 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			iter := mapiterinit(code.Type, uptr)
-			ctx.KeepRefs = append(ctx.KeepRefs, iter)
-			store(ctxptr, code.ElemIdx, 0)
-			store(ctxptr, code.Length, uintptr(mlen))
-			store(ctxptr, code.MapIter, uintptr(iter))
+			mapCtx := encoder.NewMapContext(mlen)
+			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 {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
-				mapCtx := encoder.NewMapContext(mlen)
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-				store(ctxptr, code.End.MapPos, uintptr(unsafe.Pointer(mapCtx)))
+				mapCtx.Start = len(b)
+				mapCtx.First = len(b)
 			}
-			key := mapiterkey(iter)
+			key := mapiterkey(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(key))
 			code = code.Next
 		case encoder.OpMapKey:
-			idx := load(ctxptr, code.ElemIdx)
-			length := load(ctxptr, code.Length)
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
+			idx := mapCtx.Idx
 			idx++
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
-				if idx < length {
+				if idx < mapCtx.Len {
 					b = appendMapKeyIndent(ctx, code, b)
-					store(ctxptr, code.ElemIdx, idx)
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					key := mapiterkey(iter)
+					mapCtx.Idx = int(idx)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
 					b = appendObjectEnd(ctx, code, b)
+					encoder.ReleaseMapContext(mapCtx)
 					code = code.End.Next
 				}
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				if idx < length {
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					store(ctxptr, code.ElemIdx, idx)
-					key := mapiterkey(iter)
+				mapCtx.Slice.Items[mapCtx.Idx].Value = b[mapCtx.Start:len(b)]
+				if idx < mapCtx.Len {
+					mapCtx.Idx = int(idx)
+					mapCtx.Start = len(b)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
@@ -452,46 +445,27 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				}
 			}
 		case encoder.OpMapValue:
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
 				b = appendColon(ctx, b)
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
+				mapCtx.Slice.Items[mapCtx.Idx].Key = b[mapCtx.Start:len(b)]
+				mapCtx.Start = len(b)
 			}
-			ptr := load(ctxptr, code.MapIter)
-			iter := ptrToUnsafePtr(ptr)
-			value := mapitervalue(iter)
+			value := mapitervalue(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(value))
-			mapiternext(iter)
+			mapiternext(&mapCtx.Iter)
 			code = code.Next
 		case encoder.OpMapEnd:
 			// this operation only used by sorted map.
-			length := int(load(ctxptr, code.Length))
-			ptr := load(ctxptr, code.MapPos)
-			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-			pos := mapCtx.Pos
-			for i := 0; i < length; i++ {
-				startKey := pos[i*2]
-				startValue := pos[i*2+1]
-				var endValue int
-				if i+1 < length {
-					endValue = pos[i*2+2]
-				} else {
-					endValue = len(b)
-				}
-				mapCtx.Slice.Items = append(mapCtx.Slice.Items, encoder.MapItem{
-					Key:   b[startKey:startValue],
-					Value: b[startValue:endValue],
-				})
-			}
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			sort.Sort(mapCtx.Slice)
 			buf := mapCtx.Buf
 			for _, item := range mapCtx.Slice.Items {
 				buf = appendMapKeyValue(ctx, code, buf, item.Key, item.Value)
 			}
 			buf = appendMapEnd(ctx, code, buf)
-			b = b[:pos[0]]
+			b = b[:mapCtx.First]
 			b = append(b, buf...)
 			mapCtx.Buf = buf
 			encoder.ReleaseMapContext(mapCtx)
diff --git a/internal/go-json/encoder/vm_color/vm.go b/internal/go-json/encoder/vm_color/vm.go
index 45a7c13e07..41b326e601 100644
--- a/internal/go-json/encoder/vm_color/vm.go
+++ b/internal/go-json/encoder/vm_color/vm.go
@@ -403,48 +403,41 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			iter := mapiterinit(code.Type, uptr)
-			ctx.KeepRefs = append(ctx.KeepRefs, iter)
-			store(ctxptr, code.ElemIdx, 0)
-			store(ctxptr, code.Length, uintptr(mlen))
-			store(ctxptr, code.MapIter, uintptr(iter))
+			mapCtx := encoder.NewMapContext(mlen)
+			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 {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
-				mapCtx := encoder.NewMapContext(mlen)
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-				store(ctxptr, code.End.MapPos, uintptr(unsafe.Pointer(mapCtx)))
+				mapCtx.Start = len(b)
+				mapCtx.First = len(b)
 			}
-			key := mapiterkey(iter)
+			key := mapiterkey(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(key))
 			code = code.Next
 		case encoder.OpMapKey:
-			idx := load(ctxptr, code.ElemIdx)
-			length := load(ctxptr, code.Length)
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
+			idx := mapCtx.Idx
 			idx++
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
-				if idx < length {
+				if idx < mapCtx.Len {
 					b = appendMapKeyIndent(ctx, code, b)
-					store(ctxptr, code.ElemIdx, idx)
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					key := mapiterkey(iter)
+					mapCtx.Idx = int(idx)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
 					b = appendObjectEnd(ctx, code, b)
+					encoder.ReleaseMapContext(mapCtx)
 					code = code.End.Next
 				}
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				if idx < length {
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					store(ctxptr, code.ElemIdx, idx)
-					key := mapiterkey(iter)
+				mapCtx.Slice.Items[mapCtx.Idx].Value = b[mapCtx.Start:len(b)]
+				if idx < mapCtx.Len {
+					mapCtx.Idx = int(idx)
+					mapCtx.Start = len(b)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
@@ -452,46 +445,27 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				}
 			}
 		case encoder.OpMapValue:
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
 				b = appendColon(ctx, b)
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
+				mapCtx.Slice.Items[mapCtx.Idx].Key = b[mapCtx.Start:len(b)]
+				mapCtx.Start = len(b)
 			}
-			ptr := load(ctxptr, code.MapIter)
-			iter := ptrToUnsafePtr(ptr)
-			value := mapitervalue(iter)
+			value := mapitervalue(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(value))
-			mapiternext(iter)
+			mapiternext(&mapCtx.Iter)
 			code = code.Next
 		case encoder.OpMapEnd:
 			// this operation only used by sorted map.
-			length := int(load(ctxptr, code.Length))
-			ptr := load(ctxptr, code.MapPos)
-			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-			pos := mapCtx.Pos
-			for i := 0; i < length; i++ {
-				startKey := pos[i*2]
-				startValue := pos[i*2+1]
-				var endValue int
-				if i+1 < length {
-					endValue = pos[i*2+2]
-				} else {
-					endValue = len(b)
-				}
-				mapCtx.Slice.Items = append(mapCtx.Slice.Items, encoder.MapItem{
-					Key:   b[startKey:startValue],
-					Value: b[startValue:endValue],
-				})
-			}
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			sort.Sort(mapCtx.Slice)
 			buf := mapCtx.Buf
 			for _, item := range mapCtx.Slice.Items {
 				buf = appendMapKeyValue(ctx, code, buf, item.Key, item.Value)
 			}
 			buf = appendMapEnd(ctx, code, buf)
-			b = b[:pos[0]]
+			b = b[:mapCtx.First]
 			b = append(b, buf...)
 			mapCtx.Buf = buf
 			encoder.ReleaseMapContext(mapCtx)
diff --git a/internal/go-json/encoder/vm_color_indent/vm.go b/internal/go-json/encoder/vm_color_indent/vm.go
index 5270e11988..f3f6d0b9c1 100644
--- a/internal/go-json/encoder/vm_color_indent/vm.go
+++ b/internal/go-json/encoder/vm_color_indent/vm.go
@@ -403,48 +403,41 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			iter := mapiterinit(code.Type, uptr)
-			ctx.KeepRefs = append(ctx.KeepRefs, iter)
-			store(ctxptr, code.ElemIdx, 0)
-			store(ctxptr, code.Length, uintptr(mlen))
-			store(ctxptr, code.MapIter, uintptr(iter))
+			mapCtx := encoder.NewMapContext(mlen)
+			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 {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
-				mapCtx := encoder.NewMapContext(mlen)
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-				store(ctxptr, code.End.MapPos, uintptr(unsafe.Pointer(mapCtx)))
+				mapCtx.Start = len(b)
+				mapCtx.First = len(b)
 			}
-			key := mapiterkey(iter)
+			key := mapiterkey(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(key))
 			code = code.Next
 		case encoder.OpMapKey:
-			idx := load(ctxptr, code.ElemIdx)
-			length := load(ctxptr, code.Length)
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
+			idx := mapCtx.Idx
 			idx++
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
-				if idx < length {
+				if idx < mapCtx.Len {
 					b = appendMapKeyIndent(ctx, code, b)
-					store(ctxptr, code.ElemIdx, idx)
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					key := mapiterkey(iter)
+					mapCtx.Idx = int(idx)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
 					b = appendObjectEnd(ctx, code, b)
+					encoder.ReleaseMapContext(mapCtx)
 					code = code.End.Next
 				}
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				if idx < length {
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					store(ctxptr, code.ElemIdx, idx)
-					key := mapiterkey(iter)
+				mapCtx.Slice.Items[mapCtx.Idx].Value = b[mapCtx.Start:len(b)]
+				if idx < mapCtx.Len {
+					mapCtx.Idx = int(idx)
+					mapCtx.Start = len(b)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
@@ -452,46 +445,27 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				}
 			}
 		case encoder.OpMapValue:
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
 				b = appendColon(ctx, b)
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
+				mapCtx.Slice.Items[mapCtx.Idx].Key = b[mapCtx.Start:len(b)]
+				mapCtx.Start = len(b)
 			}
-			ptr := load(ctxptr, code.MapIter)
-			iter := ptrToUnsafePtr(ptr)
-			value := mapitervalue(iter)
+			value := mapitervalue(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(value))
-			mapiternext(iter)
+			mapiternext(&mapCtx.Iter)
 			code = code.Next
 		case encoder.OpMapEnd:
 			// this operation only used by sorted map.
-			length := int(load(ctxptr, code.Length))
-			ptr := load(ctxptr, code.MapPos)
-			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-			pos := mapCtx.Pos
-			for i := 0; i < length; i++ {
-				startKey := pos[i*2]
-				startValue := pos[i*2+1]
-				var endValue int
-				if i+1 < length {
-					endValue = pos[i*2+2]
-				} else {
-					endValue = len(b)
-				}
-				mapCtx.Slice.Items = append(mapCtx.Slice.Items, encoder.MapItem{
-					Key:   b[startKey:startValue],
-					Value: b[startValue:endValue],
-				})
-			}
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			sort.Sort(mapCtx.Slice)
 			buf := mapCtx.Buf
 			for _, item := range mapCtx.Slice.Items {
 				buf = appendMapKeyValue(ctx, code, buf, item.Key, item.Value)
 			}
 			buf = appendMapEnd(ctx, code, buf)
-			b = b[:pos[0]]
+			b = b[:mapCtx.First]
 			b = append(b, buf...)
 			mapCtx.Buf = buf
 			encoder.ReleaseMapContext(mapCtx)
diff --git a/internal/go-json/encoder/vm_indent/vm.go b/internal/go-json/encoder/vm_indent/vm.go
index a73416034e..88d925c814 100644
--- a/internal/go-json/encoder/vm_indent/vm.go
+++ b/internal/go-json/encoder/vm_indent/vm.go
@@ -403,48 +403,41 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				break
 			}
 			b = appendStructHead(ctx, b)
-			iter := mapiterinit(code.Type, uptr)
-			ctx.KeepRefs = append(ctx.KeepRefs, iter)
-			store(ctxptr, code.ElemIdx, 0)
-			store(ctxptr, code.Length, uintptr(mlen))
-			store(ctxptr, code.MapIter, uintptr(iter))
+			mapCtx := encoder.NewMapContext(mlen)
+			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 {
 				b = appendMapKeyIndent(ctx, code.Next, b)
 			} else {
-				mapCtx := encoder.NewMapContext(mlen)
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				ctx.KeepRefs = append(ctx.KeepRefs, unsafe.Pointer(mapCtx))
-				store(ctxptr, code.End.MapPos, uintptr(unsafe.Pointer(mapCtx)))
+				mapCtx.Start = len(b)
+				mapCtx.First = len(b)
 			}
-			key := mapiterkey(iter)
+			key := mapiterkey(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(key))
 			code = code.Next
 		case encoder.OpMapKey:
-			idx := load(ctxptr, code.ElemIdx)
-			length := load(ctxptr, code.Length)
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
+			idx := mapCtx.Idx
 			idx++
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
-				if idx < length {
+				if idx < mapCtx.Len {
 					b = appendMapKeyIndent(ctx, code, b)
-					store(ctxptr, code.ElemIdx, idx)
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					key := mapiterkey(iter)
+					mapCtx.Idx = int(idx)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
 					b = appendObjectEnd(ctx, code, b)
+					encoder.ReleaseMapContext(mapCtx)
 					code = code.End.Next
 				}
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
-				if idx < length {
-					ptr := load(ctxptr, code.MapIter)
-					iter := ptrToUnsafePtr(ptr)
-					store(ctxptr, code.ElemIdx, idx)
-					key := mapiterkey(iter)
+				mapCtx.Slice.Items[mapCtx.Idx].Value = b[mapCtx.Start:len(b)]
+				if idx < mapCtx.Len {
+					mapCtx.Idx = int(idx)
+					mapCtx.Start = len(b)
+					key := mapiterkey(&mapCtx.Iter)
 					store(ctxptr, code.Next.Idx, uintptr(key))
 					code = code.Next
 				} else {
@@ -452,46 +445,27 @@ func Run(ctx *encoder.RuntimeContext, b []byte, codeSet *encoder.OpcodeSet) ([]b
 				}
 			}
 		case encoder.OpMapValue:
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			if (ctx.Option.Flag & encoder.UnorderedMapOption) != 0 {
 				b = appendColon(ctx, b)
 			} else {
-				ptr := load(ctxptr, code.End.MapPos)
-				mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-				mapCtx.Pos = append(mapCtx.Pos, len(b))
+				mapCtx.Slice.Items[mapCtx.Idx].Key = b[mapCtx.Start:len(b)]
+				mapCtx.Start = len(b)
 			}
-			ptr := load(ctxptr, code.MapIter)
-			iter := ptrToUnsafePtr(ptr)
-			value := mapitervalue(iter)
+			value := mapitervalue(&mapCtx.Iter)
 			store(ctxptr, code.Next.Idx, uintptr(value))
-			mapiternext(iter)
+			mapiternext(&mapCtx.Iter)
 			code = code.Next
 		case encoder.OpMapEnd:
 			// this operation only used by sorted map.
-			length := int(load(ctxptr, code.Length))
-			ptr := load(ctxptr, code.MapPos)
-			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(ptr))
-			pos := mapCtx.Pos
-			for i := 0; i < length; i++ {
-				startKey := pos[i*2]
-				startValue := pos[i*2+1]
-				var endValue int
-				if i+1 < length {
-					endValue = pos[i*2+2]
-				} else {
-					endValue = len(b)
-				}
-				mapCtx.Slice.Items = append(mapCtx.Slice.Items, encoder.MapItem{
-					Key:   b[startKey:startValue],
-					Value: b[startValue:endValue],
-				})
-			}
+			mapCtx := (*encoder.MapContext)(ptrToUnsafePtr(load(ctxptr, code.Idx)))
 			sort.Sort(mapCtx.Slice)
 			buf := mapCtx.Buf
 			for _, item := range mapCtx.Slice.Items {
 				buf = appendMapKeyValue(ctx, code, buf, item.Key, item.Value)
 			}
 			buf = appendMapEnd(ctx, code, buf)
-			b = b[:pos[0]]
+			b = b[:mapCtx.First]
 			b = append(b, buf...)
 			mapCtx.Buf = buf
 			encoder.ReleaseMapContext(mapCtx)