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package rardecode
import (
"io"
"math/bits"
)
type bitReader interface {
readBits(n uint8) (int, error) // read n bits of data
unreadBits(n uint8) // revert the reading of the last n bits read
}
// rar5BitReader is a bitReader that reads bytes from a byteReader and stops with io.EOF after l bits.
type rar5BitReader struct {
r byteReader
v int // cache of bits read from r
l int // number of bits (not cached) that can be read from r
n uint8 // number of unread bits in v
}
func (r *rar5BitReader) unreadBits(n uint8) { r.n += n }
// ReadByte reads and returns a single byte. If no byte is available, returns an error.
func (r *rar5BitReader) ReadByte() (byte, error) {
if r.n == 0 {
return r.r.ReadByte()
}
b, err := r.readBits(8)
return byte(b), err
}
func (r *rar5BitReader) reset(br byteReader) {
r.r = br
}
// setLimit sets the maximum bit count that can be read.
func (r *rar5BitReader) setLimit(n int) {
r.l = n
r.n = 0
}
// readBits returns n bits from the underlying byteReader.
// n must be less than integer size - 8.
func (r *rar5BitReader) readBits(n uint8) (int, error) {
for n > r.n {
if r.l == 0 {
// reached bits limit
return 0, io.EOF
}
c, err := r.r.ReadByte()
if err != nil {
if err == io.EOF {
// io.EOF before we reached bit limit
err = ErrDecoderOutOfData
}
return 0, err
}
r.v = r.v<<8 | int(c)
r.n += 8
r.l -= 8
if r.l < 0 {
// overshot, discard the extra bits
bits := uint8(-r.l)
r.l = 0
r.v >>= bits
r.n -= bits
}
}
r.n -= n
return (r.v >> r.n) & ((1 << n) - 1), nil
}
// rarBitReader wraps an io.ByteReader to perform various bit and byte
// reading utility functions used in RAR file processing.
type rarBitReader struct {
r byteReader
v int
n uint8
}
func (r *rarBitReader) reset(br byteReader) {
r.r = br
r.n = 0
r.v = 0
}
// readBits returns n bits from the underlying byteReader.
// n must be less than integer size - 8.
func (r *rarBitReader) readBits(n uint8) (int, error) {
for n > r.n {
b, err := r.r.ReadByte()
if err != nil {
return 0, err
}
r.v = r.v<<8 | int(b)
r.n += 8
}
r.n -= n
return (r.v >> r.n) & ((1 << n) - 1), nil
}
func (r *rarBitReader) unreadBits(n uint8) {
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 {
if bits.UintSize == 32 {
if n == 3 {
// 32bit platforms may not be able to read 32 bits as r.v
// will need up to 7 extra bits for overflow from reading a byte.
// Split it into two reads.
n, err = r.readBits(16)
if err != nil {
return 0, err
}
m := uint32(n) << 16
n, err = r.readBits(16)
return m | uint32(n), err
}
}
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) {
if r.n == 0 {
return r.r.ReadByte()
}
b, err := r.readBits(8)
return byte(b), err
}
func (r *rarBitReader) Read(p []byte) (int, error) {
if r.n == 0 {
return r.r.Read(p)
}
for i := range p {
b, err := r.readBits(8)
if err != nil {
return i, err
}
p[i] = byte(b)
}
return len(p), nil
}
func newRarBitReader(r byteReader) *rarBitReader {
return &rarBitReader{r: r}
}
|
