Add static domain security state generator tool.

net/tools/domain_security_preload_generator/trie/trie_bit_buffer.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_TRIE_TRIE_BIT_BUFFER_H_
+#define NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_TRIE_TRIE_BIT_BUFFER_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "net/tools/domain_security_preload_generator/huffman/huffman_frequency_tracker.h"
+
+namespace net {
+
+namespace transport_security_state {
+
+class BitWriter;
+
+// TrieBitBuffer acts as a buffer for TrieWriter. It can be used to write bits,
+// characters, and positions. The characters are stored as their
+// HuffmanRepresentation. Positions are references to other locations in the
+// trie.
+class TrieBitBuffer {
+ public:
+  TrieBitBuffer();
+  ~TrieBitBuffer();
+
+  // Writes |bit| to the buffer.
+  void WriteBit(uint8_t bit);
+
+  // Writes the |number_of_bits| least-significant bits from |bits| to the
+  // buffer.
+  void WriteBits(uint32_t bits, uint8_t number_of_bits);
+
+  // Write a position to the buffer. Actually writes the difference between
+  // |position| and |last_position|. |*last_position| will be updated to equal
+  // the input |position|.
+  void WritePosition(uint32_t position, int32_t* last_position);
+
+  // Writes the character in |byte| to the buffer using its Huffman
+  // representation in |table|. Optionally tracks usage of the character in
+  // |*tracker|.
+  void WriteChar(uint8_t byte,
+                 const HuffmanRepresentationTable& table,
+                 HuffmanFrequencyTracker* tracker);
+
+  // Writes the entire buffer to |*writer|. Returns the position |*writer| was
+  // at before the buffer was written to it.
+  uint32_t WriteToBitWriter(BitWriter* writer);
+
+  // Appends the buffered bits in |current_byte_| to |elements_|. Empty bits
+  // are filled with zero's.
+  void Flush();
+
+ private:
+  // Represents either the |number_of_bits| least-significant bits in |bits| or
+  // a position (offset) in the trie.
+  struct BitsOrPosition {
+    uint8_t bits;
+    uint8_t number_of_bits;
+    uint32_t position;
+  };
+
+  // Returns the minimum number of bits needed to represent |input|.
+  uint8_t BitLength(uint32_t input) const;
+
+  // Append a new element to |elements_|.
+  void AppendBitsElement(uint8_t bits, uint8_t number_of_bits);
+  void AppendPositionElement(uint32_t position);
+
+  // Buffers bits until they fill a whole byte.
+  uint8_t current_byte_ = 0;
+
+  // The number of bits currently in |current_byte_|.
+  uint32_t used_ = 0;
+
+  std::vector<BitsOrPosition> elements_;
+};
+
+}  // namespace transport_security_state
+
+}  // namespace net
+
+#endif  // NET_TOOLS_DOMAIN_SECURITY_PRELOAD_GENERATOR_TRIE_TRIE_BIT_BUFFER_H_