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