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bitarray_encoding.go
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93 lines (84 loc) · 2.4 KB
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// Copyright (c) 2021 Hirotsuna Mizuno. All rights reserved.
// Use of this source code is governed by the MIT license that can be found in
// the LICENSE file.
package bitarray
// import ()
// MarshalBinary implements the standard encoding.BinaryMarshaler interface to
// marshal a BitArray into a binary form.
//
// This appends 0 to 7 bits padding followed by 3 bits marker indicating the
// actual number of padding LSBs at the end of the original bit array.
//
// | nBits&7 | last two bytes mark | pad |
// +---------+-----------+------------+-----+
// | 5 | 1111 1111 | 1111 1:000 | 3 |
// | 4 | 1111 1111 | 1111 -:001 | 4 |
// | 3 | 1111 1111 | 111- -:010 | 5 |
// | 2 | 1111 1111 | 11-- -:011 | 6 |
// | 1 | 1111 1111 | 1--- -:100 | 7 |
// | 0 | 1111 1111 | ---- -:101 | 8 |
// | 7 | 1111 111- | ---- -:110 | 9 |
// | 6 | 1111 11-- | ---- -:111 | 10 |
func (ba *BitArray) MarshalBinary() ([]byte, error) {
if ba.IsZero() {
return []byte{}, nil
}
nBytes := (ba.nBits + 7) >> 3
nfrac := ba.nBits & 7
marker := byte((13 - nfrac) & 7)
if nfrac == 0 || nfrac>>1 == 3 {
buf := make([]byte, nBytes+1)
if ba.b != nil {
copy(buf, ba.b)
}
buf[nBytes] = marker
return buf, nil
}
buf := make([]byte, nBytes)
if ba.b != nil {
copy(buf, ba.b)
}
buf[nBytes-1] |= marker
return buf, nil
}
// MarshalText implements the standard encoding.TextMarshaler interface to
// marshal a BitArray into a textual form. This always returns a nil error.
func (ba *BitArray) MarshalText() ([]byte, error) {
if ba.IsZero() {
return []byte{}, nil
}
sb := make([]byte, ba.nBits)
if ba.b == nil {
fill30(sb)
} else {
for i := 0; i < ba.nBits; i++ {
sb[i] = '0' + ba.b[i>>3]>>(7-i&7)&1
}
}
return sb, nil
}
// MarshalJSON implements the standard json.Marshaler interface to marshal a
// BitArray into a JSON form. This always returns a nil error.
func (ba *BitArray) MarshalJSON() ([]byte, error) {
if ba.IsZero() {
return []byte(`""`), nil
}
sb := make([]byte, ba.nBits+2)
if ba.b == nil {
fill30(sb)
} else {
for i := 0; i < ba.nBits; i++ {
sb[i+1] = '0' + ba.b[i>>3]>>(7-i&7)&1
}
}
sb[0] = '"'
sb[ba.nBits+1] = '"'
return sb, nil
}
// MarshalYAML implements the yaml.Marshaler.
func (ba *BitArray) MarshalYAML() (interface{}, error) {
if ba == nil {
return nil, nil
}
return ba.String(), nil
}