chromium/third_party/webrtc/system_wrappers/source/denormal_disabler.cc

/*
 *  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.
 */

#include "system_wrappers/include/denormal_disabler.h"

#include "rtc_base/checks.h"

namespace webrtc {
namespace {

#if defined(WEBRTC_ARCH_X86_FAMILY) && defined(__clang__)
#define WEBRTC_DENORMAL_DISABLER_X86_SUPPORTED
#endif

#if defined(WEBRTC_DENORMAL_DISABLER_X86_SUPPORTED) || \
    defined(WEBRTC_ARCH_ARM_FAMILY)
#define WEBRTC_DENORMAL_DISABLER_SUPPORTED
#endif

constexpr int kUnspecifiedStatusWord = …;

#if defined(WEBRTC_DENORMAL_DISABLER_SUPPORTED)

// Control register bit mask to disable denormals on the hardware.
#if defined(WEBRTC_DENORMAL_DISABLER_X86_SUPPORTED)
// On x86 two bits are used: flush-to-zero (FTZ) and denormals-are-zero (DAZ).
constexpr int kDenormalBitMask = …;
#elif defined(WEBRTC_ARCH_ARM_FAMILY)
// On ARM one bit is used: flush-to-zero (FTZ).
constexpr int kDenormalBitMask = 1 << 24;
#endif

// Reads the relevant CPU control register and returns its value for supported
// architectures and compilers. Otherwise returns `kUnspecifiedStatusWord`.
int ReadStatusWord() { … }

// Writes `status_word` in the relevant CPU control register if the architecture
// and the compiler are supported.
void SetStatusWord(int status_word) { … }

// Returns true if the status word indicates that denormals are enabled.
constexpr bool DenormalsEnabled(int status_word) { … }

#endif  // defined(WEBRTC_DENORMAL_DISABLER_SUPPORTED)

}  // namespace

#if defined(WEBRTC_DENORMAL_DISABLER_SUPPORTED)
DenormalDisabler::DenormalDisabler() : … { … }

DenormalDisabler::DenormalDisabler(bool enabled)
    : … { … }

bool DenormalDisabler::IsSupported() { … }

DenormalDisabler::~DenormalDisabler() { … }
#else
DenormalDisabler::DenormalDisabler() : DenormalDisabler(/*enabled=*/false) {}

DenormalDisabler::DenormalDisabler(bool enabled)
    : status_word_(kUnspecifiedStatusWord), disabling_activated_(false) {}

bool DenormalDisabler::IsSupported() {
  return false;
}

DenormalDisabler::~DenormalDisabler() = default;
#endif

}  // namespace webrtc