binary.go

Documentation: encoding/binary

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package binary implements simple translation between numbers and byte
     6  // sequences and encoding and decoding of varints.
     7  //
     8  // Numbers are translated by reading and writing fixed-size values.
     9  // A fixed-size value is either a fixed-size arithmetic
    10  // type (bool, int8, uint8, int16, float32, complex64, ...)
    11  // or an array or struct containing only fixed-size values.
    12  //
    13  // The varint functions encode and decode single integer values using
    14  // a variable-length encoding; smaller values require fewer bytes.
    15  // For a specification, see
    16  // https://developers.google.com/protocol-buffers/docs/encoding.
    17  //
    18  // This package favors simplicity over efficiency. Clients that require
    19  // high-performance serialization, especially for large data structures,
    20  // should look at more advanced solutions such as the [encoding/gob]
    21  // package or [google.golang.org/protobuf] for protocol buffers.
    22  package binary
    23  
    24  import (
    25  	"errors"
    26  	"io"
    27  	"math"
    28  	"reflect"
    29  	"sync"
    30  )
    31  
    32  // A ByteOrder specifies how to convert byte slices into
    33  // 16-, 32-, or 64-bit unsigned integers.
    34  //
    35  // It is implemented by [LittleEndian], [BigEndian], and [NativeEndian].
    36  type ByteOrder interface {
    37  	Uint16([]byte) uint16
    38  	Uint32([]byte) uint32
    39  	Uint64([]byte) uint64
    40  	PutUint16([]byte, uint16)
    41  	PutUint32([]byte, uint32)
    42  	PutUint64([]byte, uint64)
    43  	String() string
    44  }
    45  
    46  // AppendByteOrder specifies how to append 16-, 32-, or 64-bit unsigned integers
    47  // into a byte slice.
    48  //
    49  // It is implemented by [LittleEndian], [BigEndian], and [NativeEndian].
    50  type AppendByteOrder interface {
    51  	AppendUint16([]byte, uint16) []byte
    52  	AppendUint32([]byte, uint32) []byte
    53  	AppendUint64([]byte, uint64) []byte
    54  	String() string
    55  }
    56  
    57  // LittleEndian is the little-endian implementation of [ByteOrder] and [AppendByteOrder].
    58  var LittleEndian littleEndian
    59  
    60  // BigEndian is the big-endian implementation of [ByteOrder] and [AppendByteOrder].
    61  var BigEndian bigEndian
    62  
    63  type littleEndian struct{}
    64  
    65  func (littleEndian) Uint16(b []byte) uint16 {
    66  	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
    67  	return uint16(b[0]) | uint16(b[1])<<8
    68  }
    69  
    70  func (littleEndian) PutUint16(b []byte, v uint16) {
    71  	_ = b[1] // early bounds check to guarantee safety of writes below
    72  	b[0] = byte(v)
    73  	b[1] = byte(v >> 8)
    74  }
    75  
    76  func (littleEndian) AppendUint16(b []byte, v uint16) []byte {
    77  	return append(b,
    78  		byte(v),
    79  		byte(v>>8),
    80  	)
    81  }
    82  
    83  func (littleEndian) Uint32(b []byte) uint32 {
    84  	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
    85  	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
    86  }
    87  
    88  func (littleEndian) PutUint32(b []byte, v uint32) {
    89  	_ = b[3] // early bounds check to guarantee safety of writes below
    90  	b[0] = byte(v)
    91  	b[1] = byte(v >> 8)
    92  	b[2] = byte(v >> 16)
    93  	b[3] = byte(v >> 24)
    94  }
    95  
    96  func (littleEndian) AppendUint32(b []byte, v uint32) []byte {
    97  	return append(b,
    98  		byte(v),
    99  		byte(v>>8),
   100  		byte(v>>16),
   101  		byte(v>>24),
   102  	)
   103  }
   104  
   105  func (littleEndian) Uint64(b []byte) uint64 {
   106  	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   107  	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
   108  		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
   109  }
   110  
   111  func (littleEndian) PutUint64(b []byte, v uint64) {
   112  	_ = b[7] // early bounds check to guarantee safety of writes below
   113  	b[0] = byte(v)
   114  	b[1] = byte(v >> 8)
   115  	b[2] = byte(v >> 16)
   116  	b[3] = byte(v >> 24)
   117  	b[4] = byte(v >> 32)
   118  	b[5] = byte(v >> 40)
   119  	b[6] = byte(v >> 48)
   120  	b[7] = byte(v >> 56)
   121  }
   122  
   123  func (littleEndian) AppendUint64(b []byte, v uint64) []byte {
   124  	return append(b,
   125  		byte(v),
   126  		byte(v>>8),
   127  		byte(v>>16),
   128  		byte(v>>24),
   129  		byte(v>>32),
   130  		byte(v>>40),
   131  		byte(v>>48),
   132  		byte(v>>56),
   133  	)
   134  }
   135  
   136  func (littleEndian) String() string { return "LittleEndian" }
   137  
   138  func (littleEndian) GoString() string { return "binary.LittleEndian" }
   139  
   140  type bigEndian struct{}
   141  
   142  func (bigEndian) Uint16(b []byte) uint16 {
   143  	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
   144  	return uint16(b[1]) | uint16(b[0])<<8
   145  }
   146  
   147  func (bigEndian) PutUint16(b []byte, v uint16) {
   148  	_ = b[1] // early bounds check to guarantee safety of writes below
   149  	b[0] = byte(v >> 8)
   150  	b[1] = byte(v)
   151  }
   152  
   153  func (bigEndian) AppendUint16(b []byte, v uint16) []byte {
   154  	return append(b,
   155  		byte(v>>8),
   156  		byte(v),
   157  	)
   158  }
   159  
   160  func (bigEndian) Uint32(b []byte) uint32 {
   161  	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
   162  	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
   163  }
   164  
   165  func (bigEndian) PutUint32(b []byte, v uint32) {
   166  	_ = b[3] // early bounds check to guarantee safety of writes below
   167  	b[0] = byte(v >> 24)
   168  	b[1] = byte(v >> 16)
   169  	b[2] = byte(v >> 8)
   170  	b[3] = byte(v)
   171  }
   172  
   173  func (bigEndian) AppendUint32(b []byte, v uint32) []byte {
   174  	return append(b,
   175  		byte(v>>24),
   176  		byte(v>>16),
   177  		byte(v>>8),
   178  		byte(v),
   179  	)
   180  }
   181  
   182  func (bigEndian) Uint64(b []byte) uint64 {
   183  	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   184  	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
   185  		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
   186  }
   187  
   188  func (bigEndian) PutUint64(b []byte, v uint64) {
   189  	_ = b[7] // early bounds check to guarantee safety of writes below
   190  	b[0] = byte(v >> 56)
   191  	b[1] = byte(v >> 48)
   192  	b[2] = byte(v >> 40)
   193  	b[3] = byte(v >> 32)
   194  	b[4] = byte(v >> 24)
   195  	b[5] = byte(v >> 16)
   196  	b[6] = byte(v >> 8)
   197  	b[7] = byte(v)
   198  }
   199  
   200  func (bigEndian) AppendUint64(b []byte, v uint64) []byte {
   201  	return append(b,
   202  		byte(v>>56),
   203  		byte(v>>48),
   204  		byte(v>>40),
   205  		byte(v>>32),
   206  		byte(v>>24),
   207  		byte(v>>16),
   208  		byte(v>>8),
   209  		byte(v),
   210  	)
   211  }
   212  
   213  func (bigEndian) String() string { return "BigEndian" }
   214  
   215  func (bigEndian) GoString() string { return "binary.BigEndian" }
   216  
   217  func (nativeEndian) String() string { return "NativeEndian" }
   218  
   219  func (nativeEndian) GoString() string { return "binary.NativeEndian" }
   220  
   221  // Read reads structured binary data from r into data.
   222  // Data must be a pointer to a fixed-size value or a slice
   223  // of fixed-size values.
   224  // Bytes read from r are decoded using the specified byte order
   225  // and written to successive fields of the data.
   226  // When decoding boolean values, a zero byte is decoded as false, and
   227  // any other non-zero byte is decoded as true.
   228  // When reading into structs, the field data for fields with
   229  // blank (_) field names is skipped; i.e., blank field names
   230  // may be used for padding.
   231  // When reading into a struct, all non-blank fields must be exported
   232  // or Read may panic.
   233  //
   234  // The error is [io.EOF] only if no bytes were read.
   235  // If an [io.EOF] happens after reading some but not all the bytes,
   236  // Read returns [io.ErrUnexpectedEOF].
   237  func Read(r io.Reader, order ByteOrder, data any) error {
   238  	// Fast path for basic types and slices.
   239  	if n := intDataSize(data); n != 0 {
   240  		bs := make([]byte, n)
   241  		if _, err := io.ReadFull(r, bs); err != nil {
   242  			return err
   243  		}
   244  		switch data := data.(type) {
   245  		case *bool:
   246  			*data = bs[0] != 0
   247  		case *int8:
   248  			*data = int8(bs[0])
   249  		case *uint8:
   250  			*data = bs[0]
   251  		case *int16:
   252  			*data = int16(order.Uint16(bs))
   253  		case *uint16:
   254  			*data = order.Uint16(bs)
   255  		case *int32:
   256  			*data = int32(order.Uint32(bs))
   257  		case *uint32:
   258  			*data = order.Uint32(bs)
   259  		case *int64:
   260  			*data = int64(order.Uint64(bs))
   261  		case *uint64:
   262  			*data = order.Uint64(bs)
   263  		case *float32:
   264  			*data = math.Float32frombits(order.Uint32(bs))
   265  		case *float64:
   266  			*data = math.Float64frombits(order.Uint64(bs))
   267  		case []bool:
   268  			for i, x := range bs { // Easier to loop over the input for 8-bit values.
   269  				data[i] = x != 0
   270  			}
   271  		case []int8:
   272  			for i, x := range bs {
   273  				data[i] = int8(x)
   274  			}
   275  		case []uint8:
   276  			copy(data, bs)
   277  		case []int16:
   278  			for i := range data {
   279  				data[i] = int16(order.Uint16(bs[2*i:]))
   280  			}
   281  		case []uint16:
   282  			for i := range data {
   283  				data[i] = order.Uint16(bs[2*i:])
   284  			}
   285  		case []int32:
   286  			for i := range data {
   287  				data[i] = int32(order.Uint32(bs[4*i:]))
   288  			}
   289  		case []uint32:
   290  			for i := range data {
   291  				data[i] = order.Uint32(bs[4*i:])
   292  			}
   293  		case []int64:
   294  			for i := range data {
   295  				data[i] = int64(order.Uint64(bs[8*i:]))
   296  			}
   297  		case []uint64:
   298  			for i := range data {
   299  				data[i] = order.Uint64(bs[8*i:])
   300  			}
   301  		case []float32:
   302  			for i := range data {
   303  				data[i] = math.Float32frombits(order.Uint32(bs[4*i:]))
   304  			}
   305  		case []float64:
   306  			for i := range data {
   307  				data[i] = math.Float64frombits(order.Uint64(bs[8*i:]))
   308  			}
   309  		default:
   310  			n = 0 // fast path doesn't apply
   311  		}
   312  		if n != 0 {
   313  			return nil
   314  		}
   315  	}
   316  
   317  	// Fallback to reflect-based decoding.
   318  	v := reflect.ValueOf(data)
   319  	size := -1
   320  	switch v.Kind() {
   321  	case reflect.Pointer:
   322  		v = v.Elem()
   323  		size = dataSize(v)
   324  	case reflect.Slice:
   325  		size = dataSize(v)
   326  	}
   327  	if size < 0 {
   328  		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
   329  	}
   330  	d := &decoder{order: order, buf: make([]byte, size)}
   331  	if _, err := io.ReadFull(r, d.buf); err != nil {
   332  		return err
   333  	}
   334  	d.value(v)
   335  	return nil
   336  }
   337  
   338  // Write writes the binary representation of data into w.
   339  // Data must be a fixed-size value or a slice of fixed-size
   340  // values, or a pointer to such data.
   341  // Boolean values encode as one byte: 1 for true, and 0 for false.
   342  // Bytes written to w are encoded using the specified byte order
   343  // and read from successive fields of the data.
   344  // When writing structs, zero values are written for fields
   345  // with blank (_) field names.
   346  func Write(w io.Writer, order ByteOrder, data any) error {
   347  	// Fast path for basic types and slices.
   348  	if n := intDataSize(data); n != 0 {
   349  		bs := make([]byte, n)
   350  		switch v := data.(type) {
   351  		case *bool:
   352  			if *v {
   353  				bs[0] = 1
   354  			} else {
   355  				bs[0] = 0
   356  			}
   357  		case bool:
   358  			if v {
   359  				bs[0] = 1
   360  			} else {
   361  				bs[0] = 0
   362  			}
   363  		case []bool:
   364  			for i, x := range v {
   365  				if x {
   366  					bs[i] = 1
   367  				} else {
   368  					bs[i] = 0
   369  				}
   370  			}
   371  		case *int8:
   372  			bs[0] = byte(*v)
   373  		case int8:
   374  			bs[0] = byte(v)
   375  		case []int8:
   376  			for i, x := range v {
   377  				bs[i] = byte(x)
   378  			}
   379  		case *uint8:
   380  			bs[0] = *v
   381  		case uint8:
   382  			bs[0] = v
   383  		case []uint8:
   384  			bs = v
   385  		case *int16:
   386  			order.PutUint16(bs, uint16(*v))
   387  		case int16:
   388  			order.PutUint16(bs, uint16(v))
   389  		case []int16:
   390  			for i, x := range v {
   391  				order.PutUint16(bs[2*i:], uint16(x))
   392  			}
   393  		case *uint16:
   394  			order.PutUint16(bs, *v)
   395  		case uint16:
   396  			order.PutUint16(bs, v)
   397  		case []uint16:
   398  			for i, x := range v {
   399  				order.PutUint16(bs[2*i:], x)
   400  			}
   401  		case *int32:
   402  			order.PutUint32(bs, uint32(*v))
   403  		case int32:
   404  			order.PutUint32(bs, uint32(v))
   405  		case []int32:
   406  			for i, x := range v {
   407  				order.PutUint32(bs[4*i:], uint32(x))
   408  			}
   409  		case *uint32:
   410  			order.PutUint32(bs, *v)
   411  		case uint32:
   412  			order.PutUint32(bs, v)
   413  		case []uint32:
   414  			for i, x := range v {
   415  				order.PutUint32(bs[4*i:], x)
   416  			}
   417  		case *int64:
   418  			order.PutUint64(bs, uint64(*v))
   419  		case int64:
   420  			order.PutUint64(bs, uint64(v))
   421  		case []int64:
   422  			for i, x := range v {
   423  				order.PutUint64(bs[8*i:], uint64(x))
   424  			}
   425  		case *uint64:
   426  			order.PutUint64(bs, *v)
   427  		case uint64:
   428  			order.PutUint64(bs, v)
   429  		case []uint64:
   430  			for i, x := range v {
   431  				order.PutUint64(bs[8*i:], x)
   432  			}
   433  		case *float32:
   434  			order.PutUint32(bs, math.Float32bits(*v))
   435  		case float32:
   436  			order.PutUint32(bs, math.Float32bits(v))
   437  		case []float32:
   438  			for i, x := range v {
   439  				order.PutUint32(bs[4*i:], math.Float32bits(x))
   440  			}
   441  		case *float64:
   442  			order.PutUint64(bs, math.Float64bits(*v))
   443  		case float64:
   444  			order.PutUint64(bs, math.Float64bits(v))
   445  		case []float64:
   446  			for i, x := range v {
   447  				order.PutUint64(bs[8*i:], math.Float64bits(x))
   448  			}
   449  		}
   450  		_, err := w.Write(bs)
   451  		return err
   452  	}
   453  
   454  	// Fallback to reflect-based encoding.
   455  	v := reflect.Indirect(reflect.ValueOf(data))
   456  	size := dataSize(v)
   457  	if size < 0 {
   458  		return errors.New("binary.Write: some values are not fixed-sized in type " + reflect.TypeOf(data).String())
   459  	}
   460  	buf := make([]byte, size)
   461  	e := &encoder{order: order, buf: buf}
   462  	e.value(v)
   463  	_, err := w.Write(buf)
   464  	return err
   465  }
   466  
   467  // Size returns how many bytes [Write] would generate to encode the value v, which
   468  // must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
   469  // If v is neither of these, Size returns -1.
   470  func Size(v any) int {
   471  	return dataSize(reflect.Indirect(reflect.ValueOf(v)))
   472  }
   473  
   474  var structSize sync.Map // map[reflect.Type]int
   475  
   476  // dataSize returns the number of bytes the actual data represented by v occupies in memory.
   477  // For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
   478  // it returns the length of the slice times the element size and does not count the memory
   479  // occupied by the header. If the type of v is not acceptable, dataSize returns -1.
   480  func dataSize(v reflect.Value) int {
   481  	switch v.Kind() {
   482  	case reflect.Slice:
   483  		if s := sizeof(v.Type().Elem()); s >= 0 {
   484  			return s * v.Len()
   485  		}
   486  
   487  	case reflect.Struct:
   488  		t := v.Type()
   489  		if size, ok := structSize.Load(t); ok {
   490  			return size.(int)
   491  		}
   492  		size := sizeof(t)
   493  		structSize.Store(t, size)
   494  		return size
   495  
   496  	default:
   497  		if v.IsValid() {
   498  			return sizeof(v.Type())
   499  		}
   500  	}
   501  
   502  	return -1
   503  }
   504  
   505  // sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
   506  func sizeof(t reflect.Type) int {
   507  	switch t.Kind() {
   508  	case reflect.Array:
   509  		if s := sizeof(t.Elem()); s >= 0 {
   510  			return s * t.Len()
   511  		}
   512  
   513  	case reflect.Struct:
   514  		sum := 0
   515  		for i, n := 0, t.NumField(); i < n; i++ {
   516  			s := sizeof(t.Field(i).Type)
   517  			if s < 0 {
   518  				return -1
   519  			}
   520  			sum += s
   521  		}
   522  		return sum
   523  
   524  	case reflect.Bool,
   525  		reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
   526  		reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   527  		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
   528  		return int(t.Size())
   529  	}
   530  
   531  	return -1
   532  }
   533  
   534  type coder struct {
   535  	order  ByteOrder
   536  	buf    []byte
   537  	offset int
   538  }
   539  
   540  type decoder coder
   541  type encoder coder
   542  
   543  func (d *decoder) bool() bool {
   544  	x := d.buf[d.offset]
   545  	d.offset++
   546  	return x != 0
   547  }
   548  
   549  func (e *encoder) bool(x bool) {
   550  	if x {
   551  		e.buf[e.offset] = 1
   552  	} else {
   553  		e.buf[e.offset] = 0
   554  	}
   555  	e.offset++
   556  }
   557  
   558  func (d *decoder) uint8() uint8 {
   559  	x := d.buf[d.offset]
   560  	d.offset++
   561  	return x
   562  }
   563  
   564  func (e *encoder) uint8(x uint8) {
   565  	e.buf[e.offset] = x
   566  	e.offset++
   567  }
   568  
   569  func (d *decoder) uint16() uint16 {
   570  	x := d.order.Uint16(d.buf[d.offset : d.offset+2])
   571  	d.offset += 2
   572  	return x
   573  }
   574  
   575  func (e *encoder) uint16(x uint16) {
   576  	e.order.PutUint16(e.buf[e.offset:e.offset+2], x)
   577  	e.offset += 2
   578  }
   579  
   580  func (d *decoder) uint32() uint32 {
   581  	x := d.order.Uint32(d.buf[d.offset : d.offset+4])
   582  	d.offset += 4
   583  	return x
   584  }
   585  
   586  func (e *encoder) uint32(x uint32) {
   587  	e.order.PutUint32(e.buf[e.offset:e.offset+4], x)
   588  	e.offset += 4
   589  }
   590  
   591  func (d *decoder) uint64() uint64 {
   592  	x := d.order.Uint64(d.buf[d.offset : d.offset+8])
   593  	d.offset += 8
   594  	return x
   595  }
   596  
   597  func (e *encoder) uint64(x uint64) {
   598  	e.order.PutUint64(e.buf[e.offset:e.offset+8], x)
   599  	e.offset += 8
   600  }
   601  
   602  func (d *decoder) int8() int8 { return int8(d.uint8()) }
   603  
   604  func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }
   605  
   606  func (d *decoder) int16() int16 { return int16(d.uint16()) }
   607  
   608  func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }
   609  
   610  func (d *decoder) int32() int32 { return int32(d.uint32()) }
   611  
   612  func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }
   613  
   614  func (d *decoder) int64() int64 { return int64(d.uint64()) }
   615  
   616  func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }
   617  
   618  func (d *decoder) value(v reflect.Value) {
   619  	switch v.Kind() {
   620  	case reflect.Array:
   621  		l := v.Len()
   622  		for i := 0; i < l; i++ {
   623  			d.value(v.Index(i))
   624  		}
   625  
   626  	case reflect.Struct:
   627  		t := v.Type()
   628  		l := v.NumField()
   629  		for i := 0; i < l; i++ {
   630  			// Note: Calling v.CanSet() below is an optimization.
   631  			// It would be sufficient to check the field name,
   632  			// but creating the StructField info for each field is
   633  			// costly (run "go test -bench=ReadStruct" and compare
   634  			// results when making changes to this code).
   635  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   636  				d.value(v)
   637  			} else {
   638  				d.skip(v)
   639  			}
   640  		}
   641  
   642  	case reflect.Slice:
   643  		l := v.Len()
   644  		for i := 0; i < l; i++ {
   645  			d.value(v.Index(i))
   646  		}
   647  
   648  	case reflect.Bool:
   649  		v.SetBool(d.bool())
   650  
   651  	case reflect.Int8:
   652  		v.SetInt(int64(d.int8()))
   653  	case reflect.Int16:
   654  		v.SetInt(int64(d.int16()))
   655  	case reflect.Int32:
   656  		v.SetInt(int64(d.int32()))
   657  	case reflect.Int64:
   658  		v.SetInt(d.int64())
   659  
   660  	case reflect.Uint8:
   661  		v.SetUint(uint64(d.uint8()))
   662  	case reflect.Uint16:
   663  		v.SetUint(uint64(d.uint16()))
   664  	case reflect.Uint32:
   665  		v.SetUint(uint64(d.uint32()))
   666  	case reflect.Uint64:
   667  		v.SetUint(d.uint64())
   668  
   669  	case reflect.Float32:
   670  		v.SetFloat(float64(math.Float32frombits(d.uint32())))
   671  	case reflect.Float64:
   672  		v.SetFloat(math.Float64frombits(d.uint64()))
   673  
   674  	case reflect.Complex64:
   675  		v.SetComplex(complex(
   676  			float64(math.Float32frombits(d.uint32())),
   677  			float64(math.Float32frombits(d.uint32())),
   678  		))
   679  	case reflect.Complex128:
   680  		v.SetComplex(complex(
   681  			math.Float64frombits(d.uint64()),
   682  			math.Float64frombits(d.uint64()),
   683  		))
   684  	}
   685  }
   686  
   687  func (e *encoder) value(v reflect.Value) {
   688  	switch v.Kind() {
   689  	case reflect.Array:
   690  		l := v.Len()
   691  		for i := 0; i < l; i++ {
   692  			e.value(v.Index(i))
   693  		}
   694  
   695  	case reflect.Struct:
   696  		t := v.Type()
   697  		l := v.NumField()
   698  		for i := 0; i < l; i++ {
   699  			// see comment for corresponding code in decoder.value()
   700  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   701  				e.value(v)
   702  			} else {
   703  				e.skip(v)
   704  			}
   705  		}
   706  
   707  	case reflect.Slice:
   708  		l := v.Len()
   709  		for i := 0; i < l; i++ {
   710  			e.value(v.Index(i))
   711  		}
   712  
   713  	case reflect.Bool:
   714  		e.bool(v.Bool())
   715  
   716  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   717  		switch v.Type().Kind() {
   718  		case reflect.Int8:
   719  			e.int8(int8(v.Int()))
   720  		case reflect.Int16:
   721  			e.int16(int16(v.Int()))
   722  		case reflect.Int32:
   723  			e.int32(int32(v.Int()))
   724  		case reflect.Int64:
   725  			e.int64(v.Int())
   726  		}
   727  
   728  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   729  		switch v.Type().Kind() {
   730  		case reflect.Uint8:
   731  			e.uint8(uint8(v.Uint()))
   732  		case reflect.Uint16:
   733  			e.uint16(uint16(v.Uint()))
   734  		case reflect.Uint32:
   735  			e.uint32(uint32(v.Uint()))
   736  		case reflect.Uint64:
   737  			e.uint64(v.Uint())
   738  		}
   739  
   740  	case reflect.Float32, reflect.Float64:
   741  		switch v.Type().Kind() {
   742  		case reflect.Float32:
   743  			e.uint32(math.Float32bits(float32(v.Float())))
   744  		case reflect.Float64:
   745  			e.uint64(math.Float64bits(v.Float()))
   746  		}
   747  
   748  	case reflect.Complex64, reflect.Complex128:
   749  		switch v.Type().Kind() {
   750  		case reflect.Complex64:
   751  			x := v.Complex()
   752  			e.uint32(math.Float32bits(float32(real(x))))
   753  			e.uint32(math.Float32bits(float32(imag(x))))
   754  		case reflect.Complex128:
   755  			x := v.Complex()
   756  			e.uint64(math.Float64bits(real(x)))
   757  			e.uint64(math.Float64bits(imag(x)))
   758  		}
   759  	}
   760  }
   761  
   762  func (d *decoder) skip(v reflect.Value) {
   763  	d.offset += dataSize(v)
   764  }
   765  
   766  func (e *encoder) skip(v reflect.Value) {
   767  	n := dataSize(v)
   768  	zero := e.buf[e.offset : e.offset+n]
   769  	for i := range zero {
   770  		zero[i] = 0
   771  	}
   772  	e.offset += n
   773  }
   774  
   775  // intDataSize returns the size of the data required to represent the data when encoded.
   776  // It returns zero if the type cannot be implemented by the fast path in Read or Write.
   777  func intDataSize(data any) int {
   778  	switch data := data.(type) {
   779  	case bool, int8, uint8, *bool, *int8, *uint8:
   780  		return 1
   781  	case []bool:
   782  		return len(data)
   783  	case []int8:
   784  		return len(data)
   785  	case []uint8:
   786  		return len(data)
   787  	case int16, uint16, *int16, *uint16:
   788  		return 2
   789  	case []int16:
   790  		return 2 * len(data)
   791  	case []uint16:
   792  		return 2 * len(data)
   793  	case int32, uint32, *int32, *uint32:
   794  		return 4
   795  	case []int32:
   796  		return 4 * len(data)
   797  	case []uint32:
   798  		return 4 * len(data)
   799  	case int64, uint64, *int64, *uint64:
   800  		return 8
   801  	case []int64:
   802  		return 8 * len(data)
   803  	case []uint64:
   804  		return 8 * len(data)
   805  	case float32, *float32:
   806  		return 4
   807  	case float64, *float64:
   808  		return 8
   809  	case []float32:
   810  		return 4 * len(data)
   811  	case []float64:
   812  		return 8 * len(data)
   813  	}
   814  	return 0
   815  }
   816
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