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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_PACKED_CT_EV_WHITELIST_BIT_STREAM_READER_H_
#define COMPONENTS_PACKED_CT_EV_WHITELIST_BIT_STREAM_READER_H_
#include <stddef.h>
#include <stdint.h>
#include "base/macros.h"
#include "base/strings/string_piece.h"
namespace packed_ct_ev_whitelist {
namespace internal {
// A class for reading individual bits from a packed buffer. Bits are read
// MSB-first from the stream.
// It is limited to 64-bit reads, 4GB streams and is inefficient as a design
// choice. This class should not be used frequently.
//
// It is meant for data that is is packed across bytes, necessitating the need
// to read a variable number of bits across a byte boundary.
class BitStreamReader {
public:
explicit BitStreamReader(const base::StringPiece& source);
// Reads unary-encoded number into |out|. Returns true if
// there was at least one bit to read, false otherwise.
bool ReadUnaryEncoding(uint64_t* out);
// Reads |num_bits| (up to 64) into |out|. |out| is filled from the MSB to the
// LSB. If |num_bits| is less than 64, the most significant |64 - num_bits|
// bits are unused and left as zeros. Returns true if the stream had the
// requested |num_bits|, false otherwise.
bool ReadBits(uint8_t num_bits, uint64_t* out);
// Returns the number of bits left in the stream.
uint64_t BitsLeft() const;
private:
// Reads a single bit. Within a byte, the bits are read from the MSB to the
// LSB.
uint8_t ReadBit();
// Reads a single byte.
// Precondition: The stream must be byte-aligned (current_bit_ == 7) before
// calling this function.
uint8_t ReadByte();
const base::StringPiece source_;
// Index of the byte currently being read from.
size_t current_byte_;
// Index of the last bit read within |current_byte_|. Since bits are read
// from the MSB to the LSB, this value is initialized to 7 and decremented
// after each read.
int8_t current_bit_;
DISALLOW_COPY_AND_ASSIGN(BitStreamReader);
};
} // namespace internal
} // namespace packed_ct_ev_whitelist
#endif // COMPONENTS_PACKED_CT_EV_WHITELIST_BIT_STREAM_READER_H_
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