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gitea/vendor/github.com/nwaples/rardecode/bit_reader.go

120 lines
2.4 KiB

package rardecode
import "io"
type bitReader interface {
readBits(n uint) (int, error) // read n bits of data
unreadBits(n uint) // revert the reading of the last n bits read
}
type limitedBitReader struct {
br bitReader
n int
err error // error to return if br returns EOF before all n bits have been read
}
// limitBitReader returns a bitReader that reads from br and stops with io.EOF after n bits.
// If br returns an io.EOF before reading n bits, err is returned.
func limitBitReader(br bitReader, n int, err error) bitReader {
return &limitedBitReader{br, n, err}
}
func (l *limitedBitReader) readBits(n uint) (int, error) {
if int(n) > l.n {
return 0, io.EOF
}
v, err := l.br.readBits(n)
if err == nil {
l.n -= int(n)
} else if err == io.EOF {
err = l.err
}
return v, err
}
func (l *limitedBitReader) unreadBits(n uint) {
l.n += int(n)
l.br.unreadBits(n)
}
// rarBitReader wraps an io.ByteReader to perform various bit and byte
// reading utility functions used in RAR file processing.
type rarBitReader struct {
r io.ByteReader
v int
n uint
}
func (r *rarBitReader) reset(br io.ByteReader) {
r.r = br
r.n = 0
r.v = 0
}
func (r *rarBitReader) readBits(n uint) (int, error) {
for n > r.n {
c, err := r.r.ReadByte()
if err != nil {
return 0, err
}
r.v = r.v<<8 | int(c)
r.n += 8
}
r.n -= n
return (r.v >> r.n) & ((1 << n) - 1), nil
}
func (r *rarBitReader) unreadBits(n uint) {
r.n += n
}
// alignByte aligns the current bit reading input to the next byte boundary.
func (r *rarBitReader) alignByte() {
r.n -= r.n % 8
}
// readUint32 reads a RAR V3 encoded uint32
func (r *rarBitReader) readUint32() (uint32, error) {
n, err := r.readBits(2)
if err != nil {
return 0, err
}
if n != 1 {
n, err = r.readBits(4 << uint(n))
return uint32(n), err
}
n, err = r.readBits(4)
if err != nil {
return 0, err
}
if n == 0 {
n, err = r.readBits(8)
n |= -1 << 8
return uint32(n), err
}
nlow, err := r.readBits(4)
n = n<<4 | nlow
return uint32(n), err
}
func (r *rarBitReader) ReadByte() (byte, error) {
n, err := r.readBits(8)
return byte(n), err
}
// readFull reads len(p) bytes into p. If fewer bytes are read an error is returned.
func (r *rarBitReader) readFull(p []byte) error {
for i := range p {
c, err := r.ReadByte()
if err != nil {
return err
}
p[i] = c
}
return nil
}
func newRarBitReader(r io.ByteReader) *rarBitReader {
return &rarBitReader{r: r}
}