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/*
* Copyright (C) 2011, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef DenormalDisabler_h
#define DenormalDisabler_h
#include <cmath>
#include <float.h>
namespace WebCore {
// Deal with denormals. They can very seriously impact performance on x86.
// Define HAVE_DENORMAL if we support flushing denormals to zero.
#if defined(XP_WIN) && defined(_MSC_VER)
#define HAVE_DENORMAL
#endif
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
#define HAVE_DENORMAL
#endif
#ifdef HAVE_DENORMAL
class DenormalDisabler {
public:
DenormalDisabler()
: m_savedCSR(0)
{
#if defined(XP_WIN) && defined(_MSC_VER)
// Save the current state, and set mode to flush denormals.
//
// http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly
_controlfp_s(&m_savedCSR, 0, 0);
unsigned int unused;
_controlfp_s(&unused, _DN_FLUSH, _MCW_DN);
#else
m_savedCSR = getCSR();
setCSR(m_savedCSR | 0x8040);
#endif
}
~DenormalDisabler()
{
#if defined(XP_WIN) && defined(_MSC_VER)
unsigned int unused;
_controlfp_s(&unused, m_savedCSR, _MCW_DN);
#else
setCSR(m_savedCSR);
#endif
}
// This is a nop if we can flush denormals to zero in hardware.
static inline float flushDenormalFloatToZero(float f)
{
#if defined(XP_WIN) && defined(_MSC_VER) && _M_IX86_FP
// For systems using x87 instead of sse, there's no hardware support
// to flush denormals automatically. Hence, we need to flush
// denormals to zero manually.
return (fabs(f) < FLT_MIN) ? 0.0f : f;
#else
return f;
#endif
}
private:
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
inline int getCSR()
{
int result;
asm volatile("stmxcsr %0" : "=m" (result));
return result;
}
inline void setCSR(int a)
{
int temp = a;
asm volatile("ldmxcsr %0" : : "m" (temp));
}
#endif
unsigned int m_savedCSR;
};
#else
// FIXME: add implementations for other architectures and compilers
class DenormalDisabler {
public:
DenormalDisabler() { }
// Assume the worst case that other architectures and compilers
// need to flush denormals to zero manually.
static inline float flushDenormalFloatToZero(float f)
{
return (fabs(f) < FLT_MIN) ? 0.0f : f;
}
};
#endif
} // namespace WebCore
#undef HAVE_DENORMAL
#endif // DenormalDisabler_h
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