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96 lines
1.4 KiB
Go

package bit
import (
"io"
)
type BufReader struct {
src []byte // source of data
n uint64 // bit buffer
bits uint // number of valid bits in n
err error // stored error
}
func (r *BufReader) ReadBits(bits uint) (n uint64) {
for bits > r.bits {
if len(r.src) == 0 {
r.err = io.EOF
return 0
}
r.n |= uint64(r.src[0]) << r.bits
r.src = r.src[1:]
r.bits += 8
}
n = r.n & (1<<bits - 1)
r.n >>= bits
r.bits -= bits
return
}
func (r *BufReader) ReadByte() byte {
if r.bits == 0 {
if len(r.src) == 0 {
r.err = io.EOF
return 0
}
b := r.src[0]
r.src = r.src[1:]
return b
}
return byte(r.ReadBits(8))
}
func (r *BufReader) Read(buf []byte) int {
if r.bits == 0 {
if len(r.src) < len(buf) {
r.err = io.EOF
return 0
}
copy(buf, r.src[:len(buf)])
r.src = r.src[len(buf):]
return len(buf)
}
for i := 0; i < len(buf); i++ {
b := r.ReadByte()
if r.err != nil {
return 0
}
buf[i] = b
}
return len(buf)
}
func (r *BufReader) DiscardBytes(n int) {
if r.bits == 0 {
if len(r.src) < n {
r.err = io.EOF
return
}
r.src = r.src[n:]
return
}
for r.bits > 8 {
r.bits -= 8
n -= 1
}
if len(r.src) < n {
r.err = io.EOF
return
}
r.n = uint64(r.src[n-1]) >> (8 - r.bits)
r.src = r.src[n:]
}
func (r *BufReader) SetSource(b []byte) {
r.src = b
r.bits = 0
r.err = nil
r.n = 0
}
func (r *BufReader) Err() error { return r.err }