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#include "converter/cached_connector.h"

#include "base/base.h"
#include "base/thread.h"
#include "converter/connector_interface.h"
#include "converter/sparse_connector.h"

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

inline int GetHashValue(uint16 rid, uint16 lid, int cache_size) {
  // Multiplying '3' makes the conversion speed faster.
  // The result hash value becomes reasonalbly random.
  return (3 * rid + lid) % cache_size;
}
}  // namespace

CachedConnector::CachedConnector(ConnectorInterface *connector,
                                 bool *cache_initialized,
                                 int *cache_key,
                                 int *cache_value,
                                 int cache_size)
    : connector_(connector),
      cache_initialized_(cache_initialized),
      cache_key_(cache_key),
      cache_value_(cache_value),
      cache_size_(cache_size) {}

CachedConnector::~CachedConnector() {}

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

  // We should mutex lock if HAVE_TLS is false. Mac OS doesn't support TLS.
  // However, we don't call it at this moment with the following reason.
  // 1) On desktop, we can assume that converter is executed on
  // single thread environment
  // 2) Can see about 20% performance drop with Mutex lock.

  const uint32 index = SparseConnector::EncodeKey(rid, lid);
  const int bucket = GetHashValue(rid, lid, cache_size_);
  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 mozc