src/storage/louds/louds_trie.cc

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#include "storage/louds/louds_trie.h"

#include "base/logging.h"
#include "base/port.h"
#include "storage/louds/louds.h"
#include "storage/louds/simple_succinct_bit_vector_index.h"

namespace mozc {
namespace storage {
namespace louds {

namespace {
inline int32 ReadInt32(const uint8 *data) {
  // TODO(noriyukit): static assertion for the endian.
  return *reinterpret_cast<const int32*>(data);
}
}  // namespace

bool LoudsTrie::Open(const uint8 *image) {
  // Reads a binary image data, which is compatible with rx.
  // The format is as follows:
  // [trie size: little endian 4byte int]
  // [terminal size: little endian 4byte int]
  // [num bits for each character annotated to an edge:
  //  little endian 4 byte int. Currently, this class supports only 8-bits]
  // [edge character image size: little endian 4 byte int]
  // [trie image: "trie size" bytes]
  // [terminal image: "terminal size" bytes]
  // [edge character image: "edge character image size" bytes]
  //
  // Here, "terminal" means "the node is one of the end of a word."
  // For example, if we have a trie for "aa" and "aaa", the trie looks like:
  //         [0]
  //        a/
  //       [1]
  //      a/
  //     [2]
  //    a/
  //   [3]
  // In this case, [0] and [1] are not terminal (as the original words contains
  // neither "" nor "a"), and [2] and [3] are terminal.
  const int louds_size = ReadInt32(image);
  const int terminal_size = ReadInt32(image + 4);
  const int num_character_bits = ReadInt32(image + 8);
  const int edge_character_size = ReadInt32(image + 12);
  CHECK_EQ(num_character_bits, 8);
  CHECK_GT(edge_character_size, 0);

  const uint8 *louds_image = image + 16;
  const uint8 *terminal_image = louds_image + louds_size;
  const uint8 *edge_character = terminal_image + terminal_size;

  louds_.Init(louds_image, louds_size);
  terminal_bit_vector_.Init(terminal_image, terminal_size);
  edge_character_ = reinterpret_cast<const char*>(edge_character);

  return true;
}

void LoudsTrie::Close() {
  louds_.Reset();
  terminal_bit_vector_.Reset();
  edge_character_ = nullptr;
}

bool LoudsTrie::MoveToChildByLabel(char label, Node *node) const {
  MoveToFirstChild(node);
  while (IsValidNode(*node)) {
    if (GetEdgeLabelToParentNode(*node) == label) {
      return true;
    }
    MoveToNextSibling(node);
  }
  return false;
}

bool LoudsTrie::Traverse(StringPiece key, Node *node) const {
  for (auto iter = key.begin(); iter != key.end(); ++iter) {
    if (!MoveToChildByLabel(*iter, node)) {
      return false;
    }
  }
  return true;
}

int LoudsTrie::ExactSearch(StringPiece key) const {
  Node node;  // Root
  if (Traverse(key, &node) && IsTerminalNode(node)) {
    return GetKeyIdOfTerminalNode(node);
  }
  return -1;
}

StringPiece LoudsTrie::RestoreKeyString(Node node, char *buf) const {
  // Ensure the returned StringPiece is null-terminated.
  char *const buf_end = buf + kMaxDepth;
  *buf_end = '\0';

  // Climb up the trie to the root and fill |buf| backward.
  char *ptr = buf_end;
  for (; !louds_.IsRoot(node); louds_.MoveToParent(&node)) {
    *--ptr = GetEdgeLabelToParentNode(node);
  }
  return StringPiece(ptr, buf_end - ptr);
}

}  // namespace louds
}  // namespace storage
}  // namespace mozc