src/converter/cached_connector.cc

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#include "converter/cached_connector.h"

#include "base/logging.h"
#include "base/port.h"
#include "converter/connector_interface.h"
#include "converter/sparse_connector.h"

namespace mozc {
namespace converter {
namespace {
const int kInvalidCacheKey = -1;

inline int GetHashValue(uint16 rid, uint16 lid, int hash_mask) {
  return ((3 * rid + lid) & hash_mask);
  // The above value is equivalent to:
  //  return (3 * rid + lid) % cache_size;
  // The performance is important here, as this is called so many times.

  // Multiplying '3' makes the conversion speed faster.
  // The result hash value becomes reasonalbly random.
}

inline uint32 EncodeKey(uint16 rid, uint16 lid) {
  return (static_cast<uint32>(rid) << 16) | lid;
}

}  // namespace

CachedConnector::CachedConnector(ConnectorInterface *connector, int cache_size)
    : connector_(connector),
      cache_initialized_(false),
      cache_key_(new int[cache_size]),
      cache_value_(new int[cache_size]),
      cache_size_(cache_size),
      hash_mask_(cache_size - 1) {
  // Check if the cache_size is 2^k form.
  DCHECK_EQ(0, cache_size & (cache_size - 1));
}

CachedConnector::~CachedConnector() {}

int CachedConnector::GetTransitionCost(uint16 rid, uint16 lid) const {
  InitializeCache();

  const uint32 index = EncodeKey(rid, lid);
  const int bucket = GetHashValue(rid, lid, hash_mask_);
  if (cache_key_[bucket] != index) {
    // Simply overwrite previous key/value.
    cache_key_[bucket] = index;
    cache_value_[bucket] = connector_->GetTransitionCost(rid, lid);
  }

  return cache_value_[bucket];
}

void CachedConnector::InitializeCache() const {
  if (cache_initialized_) {
    return;
  }
  VLOG(2) << "Initializing Cache for CachedConnector.";
  for (int i = 0; i < cache_size_; ++i) {
    cache_key_[i] = kInvalidCacheKey;
  }
  cache_initialized_ = true;
}

// Test code can use this method to get acceptable error.
int CachedConnector::GetResolution() const {
  return connector_->GetResolution();
}

void CachedConnector::ClearCache() {
  cache_initialized_ = false;
}

}  // namespace converter
}  // namespace mozc