gtsocial-umbx

json.go (37225B)

---

 // Copyright (c) 2012-2020 Ugorji Nwoke. All rights reserved.
 // Use of this source code is governed by a MIT license found in the LICENSE file.
 
 package codec
 
 // By default, this json support uses base64 encoding for bytes, because you cannot
 // store and read any arbitrary string in json (only unicode).
 // However, the user can configre how to encode/decode bytes.
 //
 // This library specifically supports UTF-8 for encoding and decoding only.
 //
 // Note that the library will happily encode/decode things which are not valid
 // json e.g. a map[int64]string. We do it for consistency. With valid json,
 // we will encode and decode appropriately.
 // Users can specify their map type if necessary to force it.
 //
 // We cannot use strconv.(Q|Unq)uote because json quotes/unquotes differently.
 
 import (
 	"encoding/base64"
 	"math"
 	"reflect"
 	"strconv"
 	"time"
 	"unicode"
 	"unicode/utf16"
 	"unicode/utf8"
 )
 
 //--------------------------------
 
 // jsonLits and jsonLitb are defined at the package level,
 // so they are guaranteed to be stored efficiently, making
 // for better append/string comparison/etc.
 //
 // (anecdotal evidence from some benchmarking on go 1.20 devel in 20220104)
 const jsonLits = `"true"false"null"`
 
 var jsonLitb = []byte(jsonLits)
 
 const (
 	jsonLitT = 1
 	jsonLitF = 6
 	jsonLitN = 12
 )
 
 const jsonEncodeUintSmallsString = "" +
 	"00010203040506070809" +
 	"10111213141516171819" +
 	"20212223242526272829" +
 	"30313233343536373839" +
 	"40414243444546474849" +
 	"50515253545556575859" +
 	"60616263646566676869" +
 	"70717273747576777879" +
 	"80818283848586878889" +
 	"90919293949596979899"
 
 var jsonEncodeUintSmallsStringBytes = []byte(jsonEncodeUintSmallsString)
 
 const (
 	jsonU4Chk2 = '0'
 	jsonU4Chk1 = 'a' - 10
 	jsonU4Chk0 = 'A' - 10
 )
 
 const (
 	// If !jsonValidateSymbols, decoding will be faster, by skipping some checks:
 	//   - If we see first character of null, false or true,
 	//     do not validate subsequent characters.
 	//   - e.g. if we see a n, assume null and skip next 3 characters,
 	//     and do not validate they are ull.
 	// P.S. Do not expect a significant decoding boost from this.
 	jsonValidateSymbols = true
 
 	// jsonEscapeMultiByteUnicodeSep controls whether some unicode characters
 	// that are valid json but may bomb in some contexts are escaped during encoeing.
 	//
 	// U+2028 is LINE SEPARATOR. U+2029 is PARAGRAPH SEPARATOR.
 	// Both technically valid JSON, but bomb on JSONP, so fix here unconditionally.
 	jsonEscapeMultiByteUnicodeSep = true
 
 	// jsonRecognizeBoolNullInQuotedStr is used during decoding into a blank interface{}
 	// to control whether we detect quoted values of bools and null where a map key is expected,
 	// and treat as nil, true or false.
 	jsonNakedBoolNullInQuotedStr = true
 
 	// jsonManualInlineDecRdInHotZones controls whether we manually inline some decReader calls.
 	//
 	// encode performance is at par with libraries that just iterate over bytes directly,
 	// because encWr (with inlined bytesEncAppender calls) is inlined.
 	// Conversely, decode performance suffers because decRd (with inlined bytesDecReader calls)
 	// isn't inlinable.
 	//
 	// To improve decode performamnce from json:
 	// - readn1 is only called for \u
 	// - consequently, to optimize json decoding, we specifically need inlining
 	//   for bytes use-case of some other decReader methods:
 	//   - jsonReadAsisChars, skipWhitespace (advance) and jsonReadNum
 	//   - AND THEN readn3, readn4 (for ull, rue and alse).
 	//   - (readn1 is only called when a char is escaped).
 	// - without inlining, we still pay the cost of a method invocationK, and this dominates time
 	// - To mitigate, we manually inline in hot zones
 	//   *excluding places where used sparingly (e.g. nextValueBytes, and other atypical cases)*.
 	//   - jsonReadAsisChars *only* called in: appendStringAsBytes
 	//   - advance called: everywhere
 	//   - jsonReadNum: decNumBytes, DecodeNaked
 	// - From running go test (our anecdotal findings):
 	//   - calling jsonReadAsisChars in appendStringAsBytes: 23431
 	//   - calling jsonReadNum in decNumBytes: 15251
 	//   - calling jsonReadNum in DecodeNaked: 612
 	// Consequently, we manually inline jsonReadAsisChars (in appendStringAsBytes)
 	// and jsonReadNum (in decNumbytes)
 	jsonManualInlineDecRdInHotZones = true
 
 	jsonSpacesOrTabsLen = 128
 
 	// jsonAlwaysReturnInternString = false
 )
 
 var (
 	// jsonTabs and jsonSpaces are used as caches for indents
 	jsonTabs, jsonSpaces [jsonSpacesOrTabsLen]byte
 
 	jsonCharHtmlSafeSet bitset256
 	jsonCharSafeSet     bitset256
 )
 
 func init() {
 	var i byte
 	for i = 0; i < jsonSpacesOrTabsLen; i++ {
 		jsonSpaces[i] = ' '
 		jsonTabs[i] = '\t'
 	}
 
 	// populate the safe values as true: note: ASCII control characters are (0-31)
 	// jsonCharSafeSet:     all true except (0-31) " \
 	// jsonCharHtmlSafeSet: all true except (0-31) " \ < > &
 	for i = 32; i < utf8.RuneSelf; i++ {
 		switch i {
 		case '"', '\\':
 		case '<', '>', '&':
 			jsonCharSafeSet.set(i) // = true
 		default:
 			jsonCharSafeSet.set(i)
 			jsonCharHtmlSafeSet.set(i)
 		}
 	}
 }
 
 // ----------------
 
 type jsonEncState struct {
 	di int8   // indent per: if negative, use tabs
 	d  bool   // indenting?
 	dl uint16 // indent level
 }
 
 func (x jsonEncState) captureState() interface{}   { return x }
 func (x *jsonEncState) restoreState(v interface{}) { *x = v.(jsonEncState) }
 
 type jsonEncDriver struct {
 	noBuiltInTypes
 	h *JsonHandle
 
 	// se interfaceExtWrapper
 
 	// ---- cpu cache line boundary?
 	jsonEncState
 
 	ks bool // map key as string
 	is byte // integer as string
 
 	typical bool
 	rawext  bool // rawext configured on the handle
 
 	s *bitset256 // safe set for characters (taking h.HTMLAsIs into consideration)
 
 	// buf *[]byte // used mostly for encoding []byte
 
 	// scratch buffer for: encode time, numbers, etc
 	//
 	// RFC3339Nano uses 35 chars: 2006-01-02T15:04:05.999999999Z07:00
 	// MaxUint64 uses 20 chars: 18446744073709551615
 	// floats are encoded using: f/e fmt, and -1 precision, or 1 if no fractions.
 	// This means we are limited by the number of characters for the
 	// mantissa (up to 17), exponent (up to 3), signs (up to 3), dot (up to 1), E (up to 1)
 	// for a total of 24 characters.
 	//    -xxx.yyyyyyyyyyyye-zzz
 	// Consequently, 35 characters should be sufficient for encoding time, integers or floats.
 	// We use up all the remaining bytes to make this use full cache lines.
 	b [48]byte
 
 	e Encoder
 }
 
 func (e *jsonEncDriver) encoder() *Encoder { return &e.e }
 
 func (e *jsonEncDriver) writeIndent() {
 	e.e.encWr.writen1('\n')
 	x := int(e.di) * int(e.dl)
 	if e.di < 0 {
 		x = -x
 		for x > jsonSpacesOrTabsLen {
 			e.e.encWr.writeb(jsonTabs[:])
 			x -= jsonSpacesOrTabsLen
 		}
 		e.e.encWr.writeb(jsonTabs[:x])
 	} else {
 		for x > jsonSpacesOrTabsLen {
 			e.e.encWr.writeb(jsonSpaces[:])
 			x -= jsonSpacesOrTabsLen
 		}
 		e.e.encWr.writeb(jsonSpaces[:x])
 	}
 }
 
 func (e *jsonEncDriver) WriteArrayElem() {
 	if e.e.c != containerArrayStart {
 		e.e.encWr.writen1(',')
 	}
 	if e.d {
 		e.writeIndent()
 	}
 }
 
 func (e *jsonEncDriver) WriteMapElemKey() {
 	if e.e.c != containerMapStart {
 		e.e.encWr.writen1(',')
 	}
 	if e.d {
 		e.writeIndent()
 	}
 }
 
 func (e *jsonEncDriver) WriteMapElemValue() {
 	if e.d {
 		e.e.encWr.writen2(':', ' ')
 	} else {
 		e.e.encWr.writen1(':')
 	}
 }
 
 func (e *jsonEncDriver) EncodeNil() {
 	// We always encode nil as just null (never in quotes)
 	// so we can easily decode if a nil in the json stream ie if initial token is n.
 
 	e.e.encWr.writestr(jsonLits[jsonLitN : jsonLitN+4])
 }
 
 func (e *jsonEncDriver) EncodeTime(t time.Time) {
 	// Do NOT use MarshalJSON, as it allocates internally.
 	// instead, we call AppendFormat directly, using our scratch buffer (e.b)
 
 	if t.IsZero() {
 		e.EncodeNil()
 	} else {
 		e.b[0] = '"'
 		b := fmtTime(t, time.RFC3339Nano, e.b[1:1])
 		e.b[len(b)+1] = '"'
 		e.e.encWr.writeb(e.b[:len(b)+2])
 	}
 }
 
 func (e *jsonEncDriver) EncodeExt(rv interface{}, basetype reflect.Type, xtag uint64, ext Ext) {
 	if ext == SelfExt {
 		e.e.encodeValue(baseRV(rv), e.h.fnNoExt(basetype))
 	} else if v := ext.ConvertExt(rv); v == nil {
 		e.EncodeNil()
 	} else {
 		e.e.encode(v)
 	}
 }
 
 func (e *jsonEncDriver) EncodeRawExt(re *RawExt) {
 	// only encodes re.Value (never re.Data)
 	if re.Value == nil {
 		e.EncodeNil()
 	} else {
 		e.e.encode(re.Value)
 	}
 }
 
 var jsonEncBoolStrs = [2][2]string{
 	{jsonLits[jsonLitF : jsonLitF+5], jsonLits[jsonLitT : jsonLitT+4]},
 	{jsonLits[jsonLitF-1 : jsonLitF+6], jsonLits[jsonLitT-1 : jsonLitT+5]},
 }
 
 func (e *jsonEncDriver) EncodeBool(b bool) {
 	e.e.encWr.writestr(
 		jsonEncBoolStrs[bool2int(e.ks && e.e.c == containerMapKey)%2][bool2int(b)%2])
 }
 
 // func (e *jsonEncDriver) EncodeBool(b bool) {
 // 	if e.ks && e.e.c == containerMapKey {
 // 		if b {
 // 			e.e.encWr.writestr(jsonLits[jsonLitT-1 : jsonLitT+5])
 // 		} else {
 // 			e.e.encWr.writestr(jsonLits[jsonLitF-1 : jsonLitF+6])
 // 		}
 // 	} else {
 // 		if b {
 // 			e.e.encWr.writestr(jsonLits[jsonLitT : jsonLitT+4])
 // 		} else {
 // 			e.e.encWr.writestr(jsonLits[jsonLitF : jsonLitF+5])
 // 		}
 // 	}
 // }
 
 func (e *jsonEncDriver) encodeFloat(f float64, bitsize, fmt byte, prec int8) {
 	var blen uint
 	if e.ks && e.e.c == containerMapKey {
 		blen = 2 + uint(len(strconv.AppendFloat(e.b[1:1], f, fmt, int(prec), int(bitsize))))
 		// _ = e.b[:blen]
 		e.b[0] = '"'
 		e.b[blen-1] = '"'
 		e.e.encWr.writeb(e.b[:blen])
 	} else {
 		e.e.encWr.writeb(strconv.AppendFloat(e.b[:0], f, fmt, int(prec), int(bitsize)))
 	}
 }
 
 func (e *jsonEncDriver) EncodeFloat64(f float64) {
 	if math.IsNaN(f) || math.IsInf(f, 0) {
 		e.EncodeNil()
 		return
 	}
 	fmt, prec := jsonFloatStrconvFmtPrec64(f)
 	e.encodeFloat(f, 64, fmt, prec)
 }
 
 func (e *jsonEncDriver) EncodeFloat32(f float32) {
 	if math.IsNaN(float64(f)) || math.IsInf(float64(f), 0) {
 		e.EncodeNil()
 		return
 	}
 	fmt, prec := jsonFloatStrconvFmtPrec32(f)
 	e.encodeFloat(float64(f), 32, fmt, prec)
 }
 
 func (e *jsonEncDriver) encodeUint(neg bool, quotes bool, u uint64) {
 	// copied mostly from std library: strconv
 	// this should only be called on 64bit OS.
 
 	// const smallsString = jsonEncodeUintSmallsString
 	var ss = jsonEncodeUintSmallsStringBytes
 
 	// typically, 19 or 20 bytes sufficient for decimal encoding a uint64
 	// var a [24]byte
 	var a = e.b[0:24]
 	var i = uint(len(a))
 
 	if quotes {
 		i--
 		setByteAt(a, i, '"')
 		// a[i] = '"'
 	}
 	// u guaranteed to fit into a uint (as we are not 32bit OS)
 	var is uint
 	var us = uint(u)
 	for us >= 100 {
 		is = us % 100 * 2
 		us /= 100
 		i -= 2
 		setByteAt(a, i+1, byteAt(ss, is+1))
 		setByteAt(a, i, byteAt(ss, is))
 		// a[i+1] = smallsString[is+1]
 		// a[i+0] = smallsString[is+0]
 	}
 
 	// us < 100
 	is = us * 2
 	i--
 	setByteAt(a, i, byteAt(ss, is+1))
 	// a[i] = smallsString[is+1]
 	if us >= 10 {
 		i--
 		setByteAt(a, i, byteAt(ss, is))
 		// a[i] = smallsString[is]
 	}
 	if neg {
 		i--
 		setByteAt(a, i, '-')
 		// a[i] = '-'
 	}
 	if quotes {
 		i--
 		setByteAt(a, i, '"')
 		// a[i] = '"'
 	}
 	e.e.encWr.writeb(a[i:])
 }
 
 func (e *jsonEncDriver) EncodeInt(v int64) {
 	quotes := e.is == 'A' || e.is == 'L' && (v > 1<<53 || v < -(1<<53)) ||
 		(e.ks && e.e.c == containerMapKey)
 
 	if cpu32Bit {
 		if quotes {
 			blen := 2 + len(strconv.AppendInt(e.b[1:1], v, 10))
 			e.b[0] = '"'
 			e.b[blen-1] = '"'
 			e.e.encWr.writeb(e.b[:blen])
 		} else {
 			e.e.encWr.writeb(strconv.AppendInt(e.b[:0], v, 10))
 		}
 		return
 	}
 
 	if v < 0 {
 		e.encodeUint(true, quotes, uint64(-v))
 	} else {
 		e.encodeUint(false, quotes, uint64(v))
 	}
 }
 
 func (e *jsonEncDriver) EncodeUint(v uint64) {
 	quotes := e.is == 'A' || e.is == 'L' && v > 1<<53 ||
 		(e.ks && e.e.c == containerMapKey)
 
 	if cpu32Bit {
 		// use strconv directly, as optimized encodeUint only works on 64-bit alone
 		if quotes {
 			blen := 2 + len(strconv.AppendUint(e.b[1:1], v, 10))
 			e.b[0] = '"'
 			e.b[blen-1] = '"'
 			e.e.encWr.writeb(e.b[:blen])
 		} else {
 			e.e.encWr.writeb(strconv.AppendUint(e.b[:0], v, 10))
 		}
 		return
 	}
 
 	e.encodeUint(false, quotes, v)
 }
 
 func (e *jsonEncDriver) EncodeString(v string) {
 	if e.h.StringToRaw {
 		e.EncodeStringBytesRaw(bytesView(v))
 		return
 	}
 	e.quoteStr(v)
 }
 
 func (e *jsonEncDriver) EncodeStringBytesRaw(v []byte) {
 	// if encoding raw bytes and RawBytesExt is configured, use it to encode
 	if v == nil {
 		e.EncodeNil()
 		return
 	}
 
 	if e.rawext {
 		iv := e.h.RawBytesExt.ConvertExt(v)
 		if iv == nil {
 			e.EncodeNil()
 		} else {
 			e.e.encode(iv)
 		}
 		return
 	}
 
 	slen := base64.StdEncoding.EncodedLen(len(v)) + 2
 
 	// bs := e.e.blist.check(*e.buf, n)[:slen]
 	// *e.buf = bs
 
 	bs := e.e.blist.peek(slen, false)
 	bs = bs[:slen]
 
 	base64.StdEncoding.Encode(bs[1:], v)
 	bs[len(bs)-1] = '"'
 	bs[0] = '"'
 	e.e.encWr.writeb(bs)
 }
 
 // indent is done as below:
 //   - newline and indent are added before each mapKey or arrayElem
 //   - newline and indent are added before each ending,
 //     except there was no entry (so we can have {} or [])
 
 func (e *jsonEncDriver) WriteArrayStart(length int) {
 	if e.d {
 		e.dl++
 	}
 	e.e.encWr.writen1('[')
 }
 
 func (e *jsonEncDriver) WriteArrayEnd() {
 	if e.d {
 		e.dl--
 		e.writeIndent()
 	}
 	e.e.encWr.writen1(']')
 }
 
 func (e *jsonEncDriver) WriteMapStart(length int) {
 	if e.d {
 		e.dl++
 	}
 	e.e.encWr.writen1('{')
 }
 
 func (e *jsonEncDriver) WriteMapEnd() {
 	if e.d {
 		e.dl--
 		if e.e.c != containerMapStart {
 			e.writeIndent()
 		}
 	}
 	e.e.encWr.writen1('}')
 }
 
 func (e *jsonEncDriver) quoteStr(s string) {
 	// adapted from std pkg encoding/json
 	const hex = "0123456789abcdef"
 	w := e.e.w()
 	w.writen1('"')
 	var i, start uint
 	for i < uint(len(s)) {
 		// encode all bytes < 0x20 (except \r, \n).
 		// also encode < > & to prevent security holes when served to some browsers.
 
 		// We optimize for ascii, by assumining that most characters are in the BMP
 		// and natively consumed by json without much computation.
 
 		// if 0x20 <= b && b != '\\' && b != '"' && b != '<' && b != '>' && b != '&' {
 		// if (htmlasis && jsonCharSafeSet.isset(b)) || jsonCharHtmlSafeSet.isset(b) {
 		if e.s.isset(s[i]) {
 			i++
 			continue
 		}
 		// b := s[i]
 		if s[i] < utf8.RuneSelf {
 			if start < i {
 				w.writestr(s[start:i])
 			}
 			switch s[i] {
 			case '\\', '"':
 				w.writen2('\\', s[i])
 			case '\n':
 				w.writen2('\\', 'n')
 			case '\r':
 				w.writen2('\\', 'r')
 			case '\b':
 				w.writen2('\\', 'b')
 			case '\f':
 				w.writen2('\\', 'f')
 			case '\t':
 				w.writen2('\\', 't')
 			default:
 				w.writestr(`\u00`)
 				w.writen2(hex[s[i]>>4], hex[s[i]&0xF])
 			}
 			i++
 			start = i
 			continue
 		}
 		c, size := utf8.DecodeRuneInString(s[i:])
 		if c == utf8.RuneError && size == 1 { // meaning invalid encoding (so output as-is)
 			if start < i {
 				w.writestr(s[start:i])
 			}
 			w.writestr(`\uFFFD`)
 			i++
 			start = i
 			continue
 		}
 		// U+2028 is LINE SEPARATOR. U+2029 is PARAGRAPH SEPARATOR.
 		// Both technically valid JSON, but bomb on JSONP, so fix here *unconditionally*.
 		if jsonEscapeMultiByteUnicodeSep && (c == '\u2028' || c == '\u2029') {
 			if start < i {
 				w.writestr(s[start:i])
 			}
 			w.writestr(`\u202`)
 			w.writen1(hex[c&0xF])
 			i += uint(size)
 			start = i
 			continue
 		}
 		i += uint(size)
 	}
 	if start < uint(len(s)) {
 		w.writestr(s[start:])
 	}
 	w.writen1('"')
 }
 
 func (e *jsonEncDriver) atEndOfEncode() {
 	if e.h.TermWhitespace {
 		var c byte = ' ' // default is that scalar is written, so output space
 		if e.e.c != 0 {
 			c = '\n' // for containers (map/list), output a newline
 		}
 		e.e.encWr.writen1(c)
 	}
 }
 
 // ----------
 
 type jsonDecState struct {
 	rawext bool // rawext configured on the handle
 
 	tok  uint8   // used to store the token read right after skipWhiteSpace
 	_    bool    // found null
 	_    byte    // padding
 	bstr [4]byte // scratch used for string \UXXX parsing
 
 	// scratch buffer used for base64 decoding (DecodeBytes in reuseBuf mode),
 	// or reading doubleQuoted string (DecodeStringAsBytes, DecodeNaked)
 	buf *[]byte
 }
 
 func (x jsonDecState) captureState() interface{}   { return x }
 func (x *jsonDecState) restoreState(v interface{}) { *x = v.(jsonDecState) }
 
 type jsonDecDriver struct {
 	noBuiltInTypes
 	decDriverNoopNumberHelper
 	h *JsonHandle
 
 	jsonDecState
 
 	// se  interfaceExtWrapper
 
 	// ---- cpu cache line boundary?
 
 	d Decoder
 }
 
 func (d *jsonDecDriver) descBd() (s string) { panic("descBd unsupported") }
 
 func (d *jsonDecDriver) decoder() *Decoder {
 	return &d.d
 }
 
 func (d *jsonDecDriver) ReadMapStart() int {
 	d.advance()
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return containerLenNil
 	}
 	if d.tok != '{' {
 		d.d.errorf("read map - expect char '%c' but got char '%c'", '{', d.tok)
 	}
 	d.tok = 0
 	return containerLenUnknown
 }
 
 func (d *jsonDecDriver) ReadArrayStart() int {
 	d.advance()
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return containerLenNil
 	}
 	if d.tok != '[' {
 		d.d.errorf("read array - expect char '%c' but got char '%c'", '[', d.tok)
 	}
 	d.tok = 0
 	return containerLenUnknown
 }
 
 // MARKER:
 // We attempted making sure CheckBreak can be inlined, by moving the skipWhitespace
 // call to an explicit (noinline) function call.
 // However, this forces CheckBreak to always incur a function call if there was whitespace,
 // with no clear benefit.
 
 func (d *jsonDecDriver) CheckBreak() bool {
 	d.advance()
 	return d.tok == '}' || d.tok == ']'
 }
 
 func (d *jsonDecDriver) ReadArrayElem() {
 	const xc uint8 = ','
 	if d.d.c != containerArrayStart {
 		d.advance()
 		if d.tok != xc {
 			d.readDelimError(xc)
 		}
 		d.tok = 0
 	}
 }
 
 func (d *jsonDecDriver) ReadArrayEnd() {
 	const xc uint8 = ']'
 	d.advance()
 	if d.tok != xc {
 		d.readDelimError(xc)
 	}
 	d.tok = 0
 }
 
 func (d *jsonDecDriver) ReadMapElemKey() {
 	const xc uint8 = ','
 	if d.d.c != containerMapStart {
 		d.advance()
 		if d.tok != xc {
 			d.readDelimError(xc)
 		}
 		d.tok = 0
 	}
 }
 
 func (d *jsonDecDriver) ReadMapElemValue() {
 	const xc uint8 = ':'
 	d.advance()
 	if d.tok != xc {
 		d.readDelimError(xc)
 	}
 	d.tok = 0
 }
 
 func (d *jsonDecDriver) ReadMapEnd() {
 	const xc uint8 = '}'
 	d.advance()
 	if d.tok != xc {
 		d.readDelimError(xc)
 	}
 	d.tok = 0
 }
 
 func (d *jsonDecDriver) readDelimError(xc uint8) {
 	d.d.errorf("read json delimiter - expect char '%c' but got char '%c'", xc, d.tok)
 }
 
 // MARKER: checkLit takes the readn(3|4) result as a parameter so they can be inlined.
 // We pass the array directly to errorf, as passing slice pushes past inlining threshold,
 // and passing slice also might cause allocation of the bs array on the heap.
 
 func (d *jsonDecDriver) checkLit3(got, expect [3]byte) {
 	d.tok = 0
 	if jsonValidateSymbols && got != expect {
 		d.d.errorf("expecting %s: got %s", expect, got)
 	}
 }
 
 func (d *jsonDecDriver) checkLit4(got, expect [4]byte) {
 	d.tok = 0
 	if jsonValidateSymbols && got != expect {
 		d.d.errorf("expecting %s: got %s", expect, got)
 	}
 }
 
 func (d *jsonDecDriver) skipWhitespace() {
 	d.tok = d.d.decRd.skipWhitespace()
 }
 
 func (d *jsonDecDriver) advance() {
 	if d.tok == 0 {
 		d.skipWhitespace()
 	}
 }
 
 func (d *jsonDecDriver) nextValueBytes(v []byte) []byte {
 	v, cursor := d.nextValueBytesR(v)
 	decNextValueBytesHelper{d: &d.d}.bytesRdV(&v, cursor)
 	return v
 }
 
 func (d *jsonDecDriver) nextValueBytesR(v0 []byte) (v []byte, cursor uint) {
 	v = v0
 	var h = decNextValueBytesHelper{d: &d.d}
 	dr := &d.d.decRd
 
 	consumeString := func() {
 	TOP:
 		bs := dr.jsonReadAsisChars()
 		h.appendN(&v, bs...)
 		if bs[len(bs)-1] != '"' {
 			// last char is '\', so consume next one and try again
 			h.append1(&v, dr.readn1())
 			goto TOP
 		}
 	}
 
 	d.advance()           // ignore leading whitespace
 	cursor = d.d.rb.c - 1 // cursor starts just before non-whitespace token
 
 	switch d.tok {
 	default:
 		h.appendN(&v, dr.jsonReadNum()...)
 	case 'n':
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		h.appendS(&v, jsonLits[jsonLitN:jsonLitN+4])
 	case 'f':
 		d.checkLit4([4]byte{'a', 'l', 's', 'e'}, d.d.decRd.readn4())
 		h.appendS(&v, jsonLits[jsonLitF:jsonLitF+5])
 	case 't':
 		d.checkLit3([3]byte{'r', 'u', 'e'}, d.d.decRd.readn3())
 		h.appendS(&v, jsonLits[jsonLitT:jsonLitT+4])
 	case '"':
 		h.append1(&v, '"')
 		consumeString()
 	case '{', '[':
 		var elem struct{}
 		var stack []struct{}
 
 		stack = append(stack, elem)
 
 		h.append1(&v, d.tok)
 
 		for len(stack) != 0 {
 			c := dr.readn1()
 			h.append1(&v, c)
 			switch c {
 			case '"':
 				consumeString()
 			case '{', '[':
 				stack = append(stack, elem)
 			case '}', ']':
 				stack = stack[:len(stack)-1]
 			}
 		}
 	}
 	d.tok = 0
 	return
 }
 
 func (d *jsonDecDriver) TryNil() bool {
 	d.advance()
 	// we shouldn't try to see if quoted "null" was here, right?
 	// only the plain string: `null` denotes a nil (ie not quotes)
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return true
 	}
 	return false
 }
 
 func (d *jsonDecDriver) DecodeBool() (v bool) {
 	d.advance()
 	// bool can be in quotes if and only if it's a map key
 	fquot := d.d.c == containerMapKey && d.tok == '"'
 	if fquot {
 		d.tok = d.d.decRd.readn1()
 	}
 	switch d.tok {
 	case 'f':
 		d.checkLit4([4]byte{'a', 'l', 's', 'e'}, d.d.decRd.readn4())
 		// v = false
 	case 't':
 		d.checkLit3([3]byte{'r', 'u', 'e'}, d.d.decRd.readn3())
 		v = true
 	case 'n':
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		// v = false
 	default:
 		d.d.errorf("decode bool: got first char %c", d.tok)
 		// v = false // "unreachable"
 	}
 	if fquot {
 		d.d.decRd.readn1()
 	}
 	return
 }
 
 func (d *jsonDecDriver) DecodeTime() (t time.Time) {
 	// read string, and pass the string into json.unmarshal
 	d.advance()
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return
 	}
 	d.ensureReadingString()
 	bs := d.readUnescapedString()
 	t, err := time.Parse(time.RFC3339, stringView(bs))
 	d.d.onerror(err)
 	return
 }
 
 func (d *jsonDecDriver) ContainerType() (vt valueType) {
 	// check container type by checking the first char
 	d.advance()
 
 	// optimize this, so we don't do 4 checks but do one computation.
 	// return jsonContainerSet[d.tok]
 
 	// ContainerType is mostly called for Map and Array,
 	// so this conditional is good enough (max 2 checks typically)
 	if d.tok == '{' {
 		return valueTypeMap
 	} else if d.tok == '[' {
 		return valueTypeArray
 	} else if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return valueTypeNil
 	} else if d.tok == '"' {
 		return valueTypeString
 	}
 	return valueTypeUnset
 }
 
 func (d *jsonDecDriver) decNumBytes() (bs []byte) {
 	d.advance()
 	dr := &d.d.decRd
 	if d.tok == '"' {
 		bs = dr.readUntil('"')
 	} else if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, dr.readn3())
 	} else {
 		if jsonManualInlineDecRdInHotZones {
 			if dr.bytes {
 				bs = dr.rb.jsonReadNum()
 			} else {
 				bs = dr.ri.jsonReadNum()
 			}
 		} else {
 			bs = dr.jsonReadNum()
 		}
 	}
 	d.tok = 0
 	return
 }
 
 func (d *jsonDecDriver) DecodeUint64() (u uint64) {
 	b := d.decNumBytes()
 	u, neg, ok := parseInteger_bytes(b)
 	if neg {
 		d.d.errorf("negative number cannot be decoded as uint64")
 	}
 	if !ok {
 		d.d.onerror(strconvParseErr(b, "ParseUint"))
 	}
 	return
 }
 
 func (d *jsonDecDriver) DecodeInt64() (v int64) {
 	b := d.decNumBytes()
 	u, neg, ok := parseInteger_bytes(b)
 	if !ok {
 		d.d.onerror(strconvParseErr(b, "ParseInt"))
 	}
 	if chkOvf.Uint2Int(u, neg) {
 		d.d.errorf("overflow decoding number from %s", b)
 	}
 	if neg {
 		v = -int64(u)
 	} else {
 		v = int64(u)
 	}
 	return
 }
 
 func (d *jsonDecDriver) DecodeFloat64() (f float64) {
 	var err error
 	bs := d.decNumBytes()
 	if len(bs) == 0 {
 		return
 	}
 	f, err = parseFloat64(bs)
 	d.d.onerror(err)
 	return
 }
 
 func (d *jsonDecDriver) DecodeFloat32() (f float32) {
 	var err error
 	bs := d.decNumBytes()
 	if len(bs) == 0 {
 		return
 	}
 	f, err = parseFloat32(bs)
 	d.d.onerror(err)
 	return
 }
 
 func (d *jsonDecDriver) DecodeExt(rv interface{}, basetype reflect.Type, xtag uint64, ext Ext) {
 	d.advance()
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return
 	}
 	if ext == nil {
 		re := rv.(*RawExt)
 		re.Tag = xtag
 		d.d.decode(&re.Value)
 	} else if ext == SelfExt {
 		d.d.decodeValue(baseRV(rv), d.h.fnNoExt(basetype))
 	} else {
 		d.d.interfaceExtConvertAndDecode(rv, ext)
 	}
 }
 
 func (d *jsonDecDriver) decBytesFromArray(bs []byte) []byte {
 	if bs != nil {
 		bs = bs[:0]
 	}
 	d.tok = 0
 	bs = append(bs, uint8(d.DecodeUint64()))
 	d.tok = d.d.decRd.skipWhitespace() // skip(&whitespaceCharBitset)
 	for d.tok != ']' {
 		if d.tok != ',' {
 			d.d.errorf("read array element - expect char '%c' but got char '%c'", ',', d.tok)
 		}
 		d.tok = 0
 		bs = append(bs, uint8(chkOvf.UintV(d.DecodeUint64(), 8)))
 		d.tok = d.d.decRd.skipWhitespace() // skip(&whitespaceCharBitset)
 	}
 	d.tok = 0
 	return bs
 }
 
 func (d *jsonDecDriver) DecodeBytes(bs []byte) (bsOut []byte) {
 	d.d.decByteState = decByteStateNone
 	d.advance()
 	if d.tok == 'n' {
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return nil
 	}
 	// if decoding into raw bytes, and the RawBytesExt is configured, use it to decode.
 	if d.rawext {
 		bsOut = bs
 		d.d.interfaceExtConvertAndDecode(&bsOut, d.h.RawBytesExt)
 		return
 	}
 	// check if an "array" of uint8's (see ContainerType for how to infer if an array)
 	if d.tok == '[' {
 		// bsOut, _ = fastpathTV.DecSliceUint8V(bs, true, d.d)
 		if bs == nil {
 			d.d.decByteState = decByteStateReuseBuf
 			bs = d.d.b[:]
 		}
 		return d.decBytesFromArray(bs)
 	}
 
 	// base64 encodes []byte{} as "", and we encode nil []byte as null.
 	// Consequently, base64 should decode null as a nil []byte, and "" as an empty []byte{}.
 
 	d.ensureReadingString()
 	bs1 := d.readUnescapedString()
 	slen := base64.StdEncoding.DecodedLen(len(bs1))
 	if slen == 0 {
 		bsOut = []byte{}
 	} else if slen <= cap(bs) {
 		bsOut = bs[:slen]
 	} else if bs == nil {
 		d.d.decByteState = decByteStateReuseBuf
 		bsOut = d.d.blist.check(*d.buf, slen)
 		bsOut = bsOut[:slen]
 		*d.buf = bsOut
 	} else {
 		bsOut = make([]byte, slen)
 	}
 	slen2, err := base64.StdEncoding.Decode(bsOut, bs1)
 	if err != nil {
 		d.d.errorf("error decoding base64 binary '%s': %v", bs1, err)
 	}
 	if slen != slen2 {
 		bsOut = bsOut[:slen2]
 	}
 	return
 }
 
 func (d *jsonDecDriver) DecodeStringAsBytes() (s []byte) {
 	d.d.decByteState = decByteStateNone
 	d.advance()
 
 	// common case - hoist outside the switch statement
 	if d.tok == '"' {
 		return d.dblQuoteStringAsBytes()
 	}
 
 	// handle non-string scalar: null, true, false or a number
 	switch d.tok {
 	case 'n':
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		return nil // []byte{}
 	case 'f':
 		d.checkLit4([4]byte{'a', 'l', 's', 'e'}, d.d.decRd.readn4())
 		return jsonLitb[jsonLitF : jsonLitF+5]
 	case 't':
 		d.checkLit3([3]byte{'r', 'u', 'e'}, d.d.decRd.readn3())
 		return jsonLitb[jsonLitT : jsonLitT+4]
 	default:
 		// try to parse a valid number
 		d.tok = 0
 		return d.d.decRd.jsonReadNum()
 	}
 }
 
 func (d *jsonDecDriver) ensureReadingString() {
 	if d.tok != '"' {
 		d.d.errorf("expecting string starting with '\"'; got '%c'", d.tok)
 	}
 }
 
 func (d *jsonDecDriver) readUnescapedString() (bs []byte) {
 	// d.ensureReadingString()
 	bs = d.d.decRd.readUntil('"')
 	d.tok = 0
 	return
 }
 
 func (d *jsonDecDriver) dblQuoteStringAsBytes() (buf []byte) {
 	checkUtf8 := d.h.ValidateUnicode
 	d.d.decByteState = decByteStateNone
 	// use a local buf variable, so we don't do pointer chasing within loop
 	buf = (*d.buf)[:0]
 	dr := &d.d.decRd
 	d.tok = 0
 
 	var bs []byte
 	var c byte
 	var firstTime bool = true
 
 	for {
 		if firstTime {
 			firstTime = false
 			if dr.bytes {
 				bs = dr.rb.jsonReadAsisChars()
 				if bs[len(bs)-1] == '"' {
 					d.d.decByteState = decByteStateZerocopy
 					return bs[:len(bs)-1]
 				}
 				goto APPEND
 			}
 		}
 
 		if jsonManualInlineDecRdInHotZones {
 			if dr.bytes {
 				bs = dr.rb.jsonReadAsisChars()
 			} else {
 				bs = dr.ri.jsonReadAsisChars()
 			}
 		} else {
 			bs = dr.jsonReadAsisChars()
 		}
 
 	APPEND:
 		_ = bs[0] // bounds check hint - slice must be > 0 elements
 		buf = append(buf, bs[:len(bs)-1]...)
 		c = bs[len(bs)-1]
 
 		if c == '"' {
 			break
 		}
 
 		// c is now '\'
 		c = dr.readn1()
 
 		switch c {
 		case '"', '\\', '/', '\'':
 			buf = append(buf, c)
 		case 'b':
 			buf = append(buf, '\b')
 		case 'f':
 			buf = append(buf, '\f')
 		case 'n':
 			buf = append(buf, '\n')
 		case 'r':
 			buf = append(buf, '\r')
 		case 't':
 			buf = append(buf, '\t')
 		case 'u':
 			rr := d.appendStringAsBytesSlashU()
 			if checkUtf8 && rr == unicode.ReplacementChar {
 				d.d.errorf("invalid UTF-8 character found after: %s", buf)
 			}
 			buf = append(buf, d.bstr[:utf8.EncodeRune(d.bstr[:], rr)]...)
 		default:
 			*d.buf = buf
 			d.d.errorf("unsupported escaped value: %c", c)
 		}
 	}
 	*d.buf = buf
 	d.d.decByteState = decByteStateReuseBuf
 	return
 }
 
 func (d *jsonDecDriver) appendStringAsBytesSlashU() (r rune) {
 	var rr uint32
 	var csu [2]byte
 	var cs [4]byte = d.d.decRd.readn4()
 	if rr = jsonSlashURune(cs); rr == unicode.ReplacementChar {
 		return unicode.ReplacementChar
 	}
 	r = rune(rr)
 	if utf16.IsSurrogate(r) {
 		csu = d.d.decRd.readn2()
 		cs = d.d.decRd.readn4()
 		if csu[0] == '\\' && csu[1] == 'u' {
 			if rr = jsonSlashURune(cs); rr == unicode.ReplacementChar {
 				return unicode.ReplacementChar
 			}
 			return utf16.DecodeRune(r, rune(rr))
 		}
 		return unicode.ReplacementChar
 	}
 	return
 }
 
 func jsonSlashURune(cs [4]byte) (rr uint32) {
 	for _, c := range cs {
 		// best to use explicit if-else
 		// - not a table, etc which involve memory loads, array lookup with bounds checks, etc
 		if c >= '0' && c <= '9' {
 			rr = rr*16 + uint32(c-jsonU4Chk2)
 		} else if c >= 'a' && c <= 'f' {
 			rr = rr*16 + uint32(c-jsonU4Chk1)
 		} else if c >= 'A' && c <= 'F' {
 			rr = rr*16 + uint32(c-jsonU4Chk0)
 		} else {
 			return unicode.ReplacementChar
 		}
 	}
 	return
 }
 
 func (d *jsonDecDriver) nakedNum(z *fauxUnion, bs []byte) (err error) {
 	// Note: nakedNum is NEVER called with a zero-length []byte
 	if d.h.PreferFloat {
 		z.v = valueTypeFloat
 		z.f, err = parseFloat64(bs)
 	} else {
 		err = parseNumber(bs, z, d.h.SignedInteger)
 	}
 	return
 }
 
 func (d *jsonDecDriver) DecodeNaked() {
 	z := d.d.naked()
 
 	d.advance()
 	var bs []byte
 	switch d.tok {
 	case 'n':
 		d.checkLit3([3]byte{'u', 'l', 'l'}, d.d.decRd.readn3())
 		z.v = valueTypeNil
 	case 'f':
 		d.checkLit4([4]byte{'a', 'l', 's', 'e'}, d.d.decRd.readn4())
 		z.v = valueTypeBool
 		z.b = false
 	case 't':
 		d.checkLit3([3]byte{'r', 'u', 'e'}, d.d.decRd.readn3())
 		z.v = valueTypeBool
 		z.b = true
 	case '{':
 		z.v = valueTypeMap // don't consume. kInterfaceNaked will call ReadMapStart
 	case '[':
 		z.v = valueTypeArray // don't consume. kInterfaceNaked will call ReadArrayStart
 	case '"':
 		// if a string, and MapKeyAsString, then try to decode it as a bool or number first
 		bs = d.dblQuoteStringAsBytes()
 		if jsonNakedBoolNullInQuotedStr &&
 			d.h.MapKeyAsString && len(bs) > 0 && d.d.c == containerMapKey {
 			switch string(bs) {
 			// case "null": // nil is never quoted
 			// 	z.v = valueTypeNil
 			case "true":
 				z.v = valueTypeBool
 				z.b = true
 			case "false":
 				z.v = valueTypeBool
 				z.b = false
 			default:
 				// check if a number: float, int or uint
 				if err := d.nakedNum(z, bs); err != nil {
 					z.v = valueTypeString
 					z.s = d.d.stringZC(bs)
 				}
 			}
 		} else {
 			z.v = valueTypeString
 			z.s = d.d.stringZC(bs)
 		}
 	default: // number
 		bs = d.d.decRd.jsonReadNum()
 		d.tok = 0
 		if len(bs) == 0 {
 			d.d.errorf("decode number from empty string")
 		}
 		if err := d.nakedNum(z, bs); err != nil {
 			d.d.errorf("decode number from %s: %v", bs, err)
 		}
 	}
 }
 
 //----------------------
 
 // JsonHandle is a handle for JSON encoding format.
 //
 // Json is comprehensively supported:
 //   - decodes numbers into interface{} as int, uint or float64
 //     based on how the number looks and some config parameters e.g. PreferFloat, SignedInt, etc.
 //   - decode integers from float formatted numbers e.g. 1.27e+8
 //   - decode any json value (numbers, bool, etc) from quoted strings
 //   - configurable way to encode/decode []byte .
 //     by default, encodes and decodes []byte using base64 Std Encoding
 //   - UTF-8 support for encoding and decoding
 //
 // It has better performance than the json library in the standard library,
 // by leveraging the performance improvements of the codec library.
 //
 // In addition, it doesn't read more bytes than necessary during a decode, which allows
 // reading multiple values from a stream containing json and non-json content.
 // For example, a user can read a json value, then a cbor value, then a msgpack value,
 // all from the same stream in sequence.
 //
 // Note that, when decoding quoted strings, invalid UTF-8 or invalid UTF-16 surrogate pairs are
 // not treated as an error. Instead, they are replaced by the Unicode replacement character U+FFFD.
 //
 // Note also that the float values for NaN, +Inf or -Inf are encoded as null,
 // as suggested by NOTE 4 of the ECMA-262 ECMAScript Language Specification 5.1 edition.
 // see http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf .
 type JsonHandle struct {
 	textEncodingType
 	BasicHandle
 
 	// Indent indicates how a value is encoded.
 	//   - If positive, indent by that number of spaces.
 	//   - If negative, indent by that number of tabs.
 	Indent int8
 
 	// IntegerAsString controls how integers (signed and unsigned) are encoded.
 	//
 	// Per the JSON Spec, JSON numbers are 64-bit floating point numbers.
 	// Consequently, integers > 2^53 cannot be represented as a JSON number without losing precision.
 	// This can be mitigated by configuring how to encode integers.
 	//
 	// IntegerAsString interpretes the following values:
 	//   - if 'L', then encode integers > 2^53 as a json string.
 	//   - if 'A', then encode all integers as a json string
 	//             containing the exact integer representation as a decimal.
 	//   - else    encode all integers as a json number (default)
 	IntegerAsString byte
 
 	// HTMLCharsAsIs controls how to encode some special characters to html: < > &
 	//
 	// By default, we encode them as \uXXX
 	// to prevent security holes when served from some browsers.
 	HTMLCharsAsIs bool
 
 	// PreferFloat says that we will default to decoding a number as a float.
 	// If not set, we will examine the characters of the number and decode as an
 	// integer type if it doesn't have any of the characters [.eE].
 	PreferFloat bool
 
 	// TermWhitespace says that we add a whitespace character
 	// at the end of an encoding.
 	//
 	// The whitespace is important, especially if using numbers in a context
 	// where multiple items are written to a stream.
 	TermWhitespace bool
 
 	// MapKeyAsString says to encode all map keys as strings.
 	//
 	// Use this to enforce strict json output.
 	// The only caveat is that nil value is ALWAYS written as null (never as "null")
 	MapKeyAsString bool
 
 	// _ uint64 // padding (cache line)
 
 	// Note: below, we store hardly-used items e.g. RawBytesExt.
 	// These values below may straddle a cache line, but they are hardly-used,
 	// so shouldn't contribute to false-sharing except in rare cases.
 
 	// RawBytesExt, if configured, is used to encode and decode raw bytes in a custom way.
 	// If not configured, raw bytes are encoded to/from base64 text.
 	RawBytesExt InterfaceExt
 }
 
 func (h *JsonHandle) isJson() bool { return true }
 
 // Name returns the name of the handle: json
 func (h *JsonHandle) Name() string { return "json" }
 
 func (h *JsonHandle) desc(bd byte) string { return string(bd) }
 
 func (h *JsonHandle) typical() bool {
 	return h.Indent == 0 && !h.MapKeyAsString && h.IntegerAsString != 'A' && h.IntegerAsString != 'L'
 }
 
 func (h *JsonHandle) newEncDriver() encDriver {
 	var e = &jsonEncDriver{h: h}
 	// var x []byte
 	// e.buf = &x
 	e.e.e = e
 	e.e.js = true
 	e.e.init(h)
 	e.reset()
 	return e
 }
 
 func (h *JsonHandle) newDecDriver() decDriver {
 	var d = &jsonDecDriver{h: h}
 	var x []byte
 	d.buf = &x
 	d.d.d = d
 	d.d.js = true
 	d.d.jsms = h.MapKeyAsString
 	d.d.init(h)
 	d.reset()
 	return d
 }
 
 func (e *jsonEncDriver) resetState() {
 	e.dl = 0
 }
 
 func (e *jsonEncDriver) reset() {
 	e.resetState()
 	// (htmlasis && jsonCharSafeSet.isset(b)) || jsonCharHtmlSafeSet.isset(b)
 	// cache values from the handle
 	e.typical = e.h.typical()
 	if e.h.HTMLCharsAsIs {
 		e.s = &jsonCharSafeSet
 	} else {
 		e.s = &jsonCharHtmlSafeSet
 	}
 	e.rawext = e.h.RawBytesExt != nil
 	e.di = int8(e.h.Indent)
 	e.d = e.h.Indent != 0
 	e.ks = e.h.MapKeyAsString
 	e.is = e.h.IntegerAsString
 }
 
 func (d *jsonDecDriver) resetState() {
 	*d.buf = d.d.blist.check(*d.buf, 256)
 	d.tok = 0
 }
 
 func (d *jsonDecDriver) reset() {
 	d.resetState()
 	d.rawext = d.h.RawBytesExt != nil
 }
 
 func jsonFloatStrconvFmtPrec64(f float64) (fmt byte, prec int8) {
 	fmt = 'f'
 	prec = -1
 	fbits := math.Float64bits(f)
 	abs := math.Float64frombits(fbits &^ (1 << 63))
 	if abs == 0 || abs == 1 {
 		prec = 1
 	} else if abs < 1e-6 || abs >= 1e21 {
 		fmt = 'e'
 	} else if noFrac64(fbits) {
 		prec = 1
 	}
 	return
 }
 
 func jsonFloatStrconvFmtPrec32(f float32) (fmt byte, prec int8) {
 	fmt = 'f'
 	prec = -1
 	// directly handle Modf (to get fractions) and Abs (to get absolute)
 	fbits := math.Float32bits(f)
 	abs := math.Float32frombits(fbits &^ (1 << 31))
 	if abs == 0 || abs == 1 {
 		prec = 1
 	} else if abs < 1e-6 || abs >= 1e21 {
 		fmt = 'e'
 	} else if noFrac32(fbits) {
 		prec = 1
 	}
 	return
 }
 
 var _ decDriverContainerTracker = (*jsonDecDriver)(nil)
 var _ encDriverContainerTracker = (*jsonEncDriver)(nil)
 var _ decDriver = (*jsonDecDriver)(nil)
 var _ encDriver = (*jsonEncDriver)(nil)