lazarus/streaming/bitreader.go

51 lines
854 B
Go

package streaming
import (
"errors"
"io"
)
type BitReader struct {
reader io.Reader
offset int
buffer [1]byte
}
func NewReader(reader io.Reader) *BitReader {
return &BitReader{reader: reader}
}
func (r *BitReader) ReadBits(count int) (uint64, error) {
if count > 64 {
return 0, errors.New("cannot read more than 64 bits at a time")
}
var value uint64
for count > 0 {
bitOffset := r.offset % 8
bitsLeft := 8 - bitOffset
if bitsLeft == 8 {
if _, err := r.reader.Read(r.buffer[:]); err != nil {
return 0, err
}
}
bitsRead := count
if bitsRead > bitsLeft {
bitsRead = bitsLeft
}
buffer := r.buffer[0]
buffer <<= uint(bitOffset)
buffer >>= (uint(bitOffset) + uint(bitsLeft-bitsRead))
value <<= uint(bitsRead)
value |= uint64(buffer)
r.offset += bitsRead
count -= bitsRead
}
return value, nil
}