folly/folly/docs/examples/folly/Likely.cpp

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <cstdlib>
#include <folly/Likely.h>
#include <folly/portability/GTest.h>

TEST(likely, demo) {
  int x = std::rand() % 1;
  if (FOLLY_LIKELY(x)) {
    // Compiler optimizes for this branch...
  } else {
    // ...even if this one is actually hotter
  }
}