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