denormal_disabler.h

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/*

 *  Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.

 *  Use of this source code is governed by a BSD-style license

 *  that can be found in the LICENSE file in the root of the source

 *  tree. An additional intellectual property rights grant can be found

 *  in the file PATENTS.  All contributing project authors may

 *  be found in the AUTHORS file in the root of the source tree.

*/

#ifndef SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_

#define SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_

#include "rtc_base/system/arch.h"

namespace webrtc {

// Activates the hardware (HW) way to flush denormals (see [1]) to zero as they

// can very seriously impact performance. At destruction time restores the

// denormals handling state read by the ctor; hence, supports nested calls.

// Equals a no-op if the architecture is not x86 or ARM or if the compiler is

// not CLANG.

// [1] https://en.wikipedia.org/wiki/Denormal_number

//

// Example usage:

//

// void Foo() {

//   DenormalDisabler d;

//   ...

// }

class DenormalDisabler {

 public:

  // Ctor. If architecture and compiler are supported, stores the HW settings

  // for denormals, disables denormals and sets `disabling_activated_` to true.

  // Otherwise, only sets `disabling_activated_` to false.

  DenormalDisabler();

  // Ctor. Same as above, but also requires `enabled` to be true to disable

  // denormals.

  explicit DenormalDisabler(bool enabled);

  DenormalDisabler(const DenormalDisabler&) = delete;

  DenormalDisabler& operator=(const DenormalDisabler&) = delete;

  // Dtor. If `disabling_activated_` is true, restores the denormals HW settings

  // read by the ctor before denormals were disabled. Otherwise it's a no-op.

  ~DenormalDisabler();

  // Returns true if architecture and compiler are supported.

  static bool IsSupported();

 private:

  const int status_word_;

  const bool disabling_activated_;

};

}  // namespace webrtc

#endif  // SYSTEM_WRAPPERS_INCLUDE_DENORMAL_DISABLER_H_