Add static domain security state generator tool.

net/tools/domain_security_preload_generator/bit_writer.h

+// Copyright (c) 2016 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 NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_
+#define NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+namespace net {
+
+namespace transport_security_state {
+
+// BitWriter acts as a buffer to which bits can be written. The bits are stored
+// as bytes in a vector. BitWriter will buffer bits until it contains 8 bits at
+// which point they will be appended to the vector automatically.
+class BitWriter {
+ public:
+  BitWriter();
+  ~BitWriter();
+
+  // Appends |bit| to the end of the buffer.
+  void WriteBit(uint8_t bit);
+
+  // Appends the |number_of_bits| least-significant bits of |bits| to the end of
+  // the buffer.
+  void WriteBits(uint32_t bits, uint8_t number_of_bits);
+
+  // Appends the buffered bits in |current_byte_| to the |bytes_| vector. When
+  // there are less than 8 bits in the buffer, the empty bits will be filled
+  // with zero's.
+  void Flush();
+  uint32_t position() const { return position_; }
+
+  // Returns a reference to |bytes_|. Make sure to call Flush() first so that
+  // the buffered bits are written to |bytes_| as well.
+  const std::vector<uint8_t>& bytes() const { return bytes_; }
+
+ private:
+  // Returns the minimum number of bits needed to represent |input|.
+  uint8_t BitLength(uint32_t input) const;
+
+  // Buffers bits until they fill a whole byte.
+  uint8_t current_byte_ = 0;
+
+  // The number of bits currently in |current_byte_|.
+  uint8_t used_ = 0;
+
+  // Total number of bits written to this BitWriter.
+  uint32_t position_ = 0;
+
+  std::vector<uint8_t> bytes_;
+};
+
+}  // namespace transport_security_state
+
+}  // namespace net
+
+#endif  // NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_BIT_WRITER_H_