The Tor Browser: content/media/webaudio/blink/DenormalDisabler.h@97036ab72558

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

     1 /*

     2  * Copyright (C) 2011, Google Inc. All rights reserved.

     3  *

     4  * Redistribution and use in source and binary forms, with or without

     5  * modification, are permitted provided that the following conditions

     6  * are met:

     7  * 1.  Redistributions of source code must retain the above copyright

     8  *    notice, this list of conditions and the following disclaimer.

     9  * 2.  Redistributions in binary form must reproduce the above copyright

    10  *    notice, this list of conditions and the following disclaimer in the

    11  *    documentation and/or other materials provided with the distribution.

    12  *

    13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY

    14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

    15  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

    16  * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY

    17  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

    18  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

    19  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON

    20  * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

    21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS

    22  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    23  */

    25 #ifndef DenormalDisabler_h

    26 #define DenormalDisabler_h

    28 #define _USE_MATH_DEFINES

    29 #include <cmath>

    30 #include <float.h>

    32 namespace WebCore {

    34 // Deal with denormals. They can very seriously impact performance on x86.

    36 // Define HAVE_DENORMAL if we support flushing denormals to zero.

    37 #if defined(XP_WIN) && defined(_MSC_VER)

    38 #define HAVE_DENORMAL

    39 #endif

    41 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))

    42 #define HAVE_DENORMAL

    43 #endif

    45 #ifdef HAVE_DENORMAL

    46 class DenormalDisabler {

    47 public:

    48     DenormalDisabler()

    49             : m_savedCSR(0)

    50     {

    51 #if defined(XP_WIN) && defined(_MSC_VER)

    52         // Save the current state, and set mode to flush denormals.

    53         //

    54         // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly

    55         _controlfp_s(&m_savedCSR, 0, 0);

    56         unsigned int unused;

    57         _controlfp_s(&unused, _DN_FLUSH, _MCW_DN);

    58 #else

    59         m_savedCSR = getCSR();

    60         setCSR(m_savedCSR | 0x8040);

    61 #endif

    62     }

    64     ~DenormalDisabler()

    65     {

    66 #if defined(XP_WIN) && defined(_MSC_VER)

    67         unsigned int unused;

    68         _controlfp_s(&unused, m_savedCSR, _MCW_DN);

    69 #else

    70         setCSR(m_savedCSR);

    71 #endif

    72     }

    74     // This is a nop if we can flush denormals to zero in hardware.

    75     static inline float flushDenormalFloatToZero(float f)

    76     {

    77 #if defined(XP_WIN) && defined(_MSC_VER) && _M_IX86_FP

    78         // For systems using x87 instead of sse, there's no hardware support

    79         // to flush denormals automatically. Hence, we need to flush

    80         // denormals to zero manually.

    81         return (fabs(f) < FLT_MIN) ? 0.0f : f;

    82 #else

    83         return f;

    84 #endif

    85     }

    86 private:

    87 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))

    88     inline int getCSR()

    89     {

    90         int result;

    91         asm volatile("stmxcsr %0" : "=m" (result));

    92         return result;

    93     }

    95     inline void setCSR(int a)

    96     {

    97         int temp = a;

    98         asm volatile("ldmxcsr %0" : : "m" (temp));

    99     }

   101 #endif

   103     unsigned int m_savedCSR;

   104 };

   106 #else

   107 // FIXME: add implementations for other architectures and compilers

   108 class DenormalDisabler {

   109 public:

   110     DenormalDisabler() { }

   112     // Assume the worst case that other architectures and compilers

   113     // need to flush denormals to zero manually.

   114     static inline float flushDenormalFloatToZero(float f)

   115     {

   116         return (fabs(f) < FLT_MIN) ? 0.0f : f;

   117     }

   118 };

   120 #endif

   122 } // WebCore

   124 #undef HAVE_DENORMAL

   125 #endif // DenormalDisabler_h

The Tor Browser / file revision

content/media/webaudio/blink/DenormalDisabler.h@97036ab72558

content/media/webaudio/blink/DenormalDisabler.h