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