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istream.go
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/
istream.go
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// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package encoding
import (
"io"
"github.com/m3db/m3/src/dbnode/x/xio"
)
// IStream encapsulates a readable stream.
type IStream struct {
r xio.Reader64
current uint64 // current uint64 we are working off of
index int // current index within data slice
remaining uint8 // bits remaining in current to be read
}
var (
_ io.ByteReader = (*IStream)(nil)
_ io.Reader = (*IStream)(nil)
)
// NewIStream creates a new IStream
func NewIStream(reader64 xio.Reader64) *IStream {
return &IStream{r: reader64}
}
// Read reads len(b) bytes.
func (is *IStream) Read(b []byte) (int, error) {
var i int
for ; i < len(b); i++ {
res, err := is.ReadBits(8)
if err != nil {
return i, err
}
b[i] = byte(res)
}
return i, nil
}
// ReadByte reads the next Byte.
func (is *IStream) ReadByte() (byte, error) {
res, err := is.ReadBits(8)
return byte(res), err
}
// ReadBit reads the next Bit.
func (is *IStream) ReadBit() (Bit, error) {
res, err := is.ReadBits(1)
return Bit(res), err
}
// ReadBits reads the next Bits.
func (is *IStream) ReadBits(numBits uint8) (uint64, error) {
res := is.current >> (64 - numBits)
remaining := is.remaining
if numBits <= remaining {
// Have enough bits buffered.
is.current <<= numBits
is.remaining -= numBits
return res, nil
}
// Not enough bits buffered, read next word from the stream.
bitsNeeded := numBits - remaining
current, n, err := is.r.Read64()
if err != nil {
return 0, err
}
n *= 8
if n < bitsNeeded {
return 0, io.EOF
}
is.current = current << bitsNeeded
is.remaining = n - bitsNeeded
return res | current>>(64-bitsNeeded), nil
}
// PeekBits looks at the next Bits, but doesn't move the pos.
func (is *IStream) PeekBits(numBits uint8) (uint64, error) {
if numBits <= is.remaining {
return readBitsInWord(is.current, numBits), nil
}
res := readBitsInWord(is.current, numBits)
bitsNeeded := numBits - is.remaining
next, bytes, err := is.r.Peek64()
if err != nil {
return 0, err
}
if rem := 8 * bytes; rem < bitsNeeded {
return 0, io.EOF
}
return res | readBitsInWord(next, bitsNeeded), nil
}
// RemainingBitsInCurrentByte returns the number of bits remaining to be read in the current byte.
func (is *IStream) RemainingBitsInCurrentByte() uint {
return uint(is.remaining % 8)
}
// readBitsInWord reads the first numBits in word w.
func readBitsInWord(w uint64, numBits uint8) uint64 {
return w >> (64 - numBits)
}
// Reset resets the IStream.
func (is *IStream) Reset(reader xio.Reader64) {
is.current = 0
is.remaining = 0
is.index = 0
is.r = reader
}