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hyperstone/bit/stream_reader.go

72 lines
1.5 KiB
Go

package bit
import (
"io"
)
// bit.Reader allows for bit-level reading of arbitrary source data. This is
// based on the bit reader found in the standard library's bzip2 package.
// https://golang.org/src/compress/bzip2/bit_reader.go
type streamReader struct {
src io.ByteReader // source of data
n uint64 // bit buffer
bits uint // number of valid bits in n
err error // stored error
}
// ReadBits reads the given number of bits and returns them in the
// least-significant part of a uint64.
func (r *streamReader) ReadBits(bits uint) (n uint64) {
if r.err != nil {
return 0
}
for bits > r.bits {
b, err := r.src.ReadByte()
if err != nil {
r.err = err
return 0
}
r.n |= uint64(b) << r.bits
r.bits += 8
}
n = r.n & (1<<bits - 1)
r.n >>= bits
r.bits -= bits
return
}
// ReadByte reads a single byte, regardless of alignment.
func (r *streamReader) ReadByte() byte {
if r.bits == 0 {
b, err := r.src.ReadByte()
if err != nil {
r.err = err
return 0
}
return b
}
return byte(r.ReadBits(8))
}
// Read reads like an io.Reader, taking care of alignment internally.
func (r *streamReader) Read(buf []byte) int {
for i := 0; i < len(buf); i++ {
b := r.ReadByte()
if r.err != nil {
return 0
}
buf[i] = b
}
return len(buf)
}
// discards N byte of data on the reader or until EOF
func (r *streamReader) DiscardBytes(n int) {
for i := 0; i < n; i++ {
r.ReadByte()
}
}
func (r *streamReader) Err() error { return r.err }