absl/base/internal/cycleclock_config.h

// Copyright 2022 The Abseil Authors
//
// 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
//
//     https://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.

#ifndef ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_
#define ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_

#include <cstdint>

#include "absl/base/config.h"
#include "absl/base/internal/inline_variable.h"
#include "absl/base/internal/unscaledcycleclock_config.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace base_internal {

#if ABSL_USE_UNSCALED_CYCLECLOCK
#ifdef NDEBUG
#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
// Not debug mode and the UnscaledCycleClock frequency is the CPU
// frequency.  Scale the CycleClock to prevent overflow if someone
// tries to represent the time as cycles since the Unix epoch.
ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 1);
#else
// Not debug mode and the UnscaledCycleClock isn't operating at the
// raw CPU frequency. There is no need to do any scaling, so don't
// needlessly sacrifice precision.
ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 0);
#endif
#else   // NDEBUG
// In debug mode use a different shift to discourage depending on a
// particular shift value.
ABSL_INTERNAL_INLINE_CONSTEXPR(int32_t, kCycleClockShift, 2);
#endif  // NDEBUG

ABSL_INTERNAL_INLINE_CONSTEXPR(double, kCycleClockFrequencyScale,
                               1.0 / (1 << kCycleClockShift));
#endif  //  ABSL_USE_UNSCALED_CYCLECLOC

}  // namespace base_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_BASE_INTERNAL_CYCLECLOCK_CONFIG_H_