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package bitio
import "io"
type Reader interface {
io.Reader
// alignment:
// |-1-byte-block-|--------------|--------------|--------------|
// |<-offset->|<-------------------width---------------------->|
ReadBits(width uint) (data []byte, err error)
ReadBit() (bit bool, err error)
}
type ReadSeeker interface {
Reader
io.Seeker
}
type reader struct {
reader io.Reader
octet byte
width uint
}
func NewReader(r io.Reader) Reader {
return &reader{reader: r}
}
func (r *reader) Read(p []byte) (n int, err error) {
if r.width != 0 {
return 0, ErrInvalidAlignment
}
return r.reader.Read(p)
}
func (r *reader) ReadBits(size uint) ([]byte, error) {
bytes := (size + 7) / 8
data := make([]byte, bytes)
offset := (bytes * 8) - (size)
for i := uint(0); i < size; i++ {
bit, err := r.ReadBit()
if err != nil {
return nil, err
}
byteIdx := (offset + i) / 8
bitIdx := 7 - (offset+i)%8
if bit {
data[byteIdx] |= 0x1 << bitIdx
}
}
return data, nil
}
func (r *reader) ReadBit() (bool, error) {
if r.width == 0 {
buf := make([]byte, 1)
if n, err := r.reader.Read(buf); err != nil {
return false, err
} else if n != 1 {
return false, ErrDiscouragedReader
}
r.octet = buf[0]
r.width = 8
}
r.width--
return (r.octet>>r.width)&0x01 != 0, nil
}
type readSeeker struct {
reader
seeker io.Seeker
}
func NewReadSeeker(r io.ReadSeeker) ReadSeeker {
return &readSeeker{
reader: reader{reader: r},
seeker: r,
}
}
func (r *readSeeker) Seek(offset int64, whence int) (int64, error) {
if whence == io.SeekCurrent && r.reader.width != 0 {
return 0, ErrInvalidAlignment
}
n, err := r.seeker.Seek(offset, whence)
if err != nil {
return n, err
}
r.reader.width = 0
return n, nil
}
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