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 */ 24 25#ifndef DenormalDisabler_h 26#define DenormalDisabler_h 27 28#include <wtf/MathExtras.h> 29 30namespace WebCore { 31 32// Deal with denormals. They can very seriously impact performance on x86. 33 34// Define HAVE_DENORMAL if we support flushing denormals to zero. 35#if OS(WINDOWS) && COMPILER(MSVC) 36#define HAVE_DENORMAL 37#endif 38 39#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) 40#define HAVE_DENORMAL 41#endif 42 43#ifdef HAVE_DENORMAL 44class DenormalDisabler { 45public: 46 DenormalDisabler() 47 : m_savedCSR(0) 48 { 49#if OS(WINDOWS) && COMPILER(MSVC) 50 // Save the current state, and set mode to flush denormals. 51 // 52 // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly 53 _controlfp_s(&m_savedCSR, 0, 0); 54 unsigned int unused; 55 _controlfp_s(&unused, _DN_FLUSH, _MCW_DN); 56#else 57 m_savedCSR = getCSR(); 58 setCSR(m_savedCSR | 0x8040); 59#endif 60 } 61 62 ~DenormalDisabler() 63 { 64#if OS(WINDOWS) && COMPILER(MSVC) 65 unsigned int unused; 66 _controlfp_s(&unused, m_savedCSR, _MCW_DN); 67#else 68 setCSR(m_savedCSR); 69#endif 70 } 71 72 // This is a nop if we can flush denormals to zero in hardware. 73 static inline float flushDenormalFloatToZero(float f) 74 { 75#if OS(WINDOWS) && COMPILER(MSVC) && (!_M_IX86_FP) 76 // For systems using x87 instead of sse, there's no hardware support 77 // to flush denormals automatically. Hence, we need to flush 78 // denormals to zero manually. 79 return (fabs(f) < FLT_MIN) ? 0.0f : f; 80#else 81 return f; 82#endif 83 } 84private: 85#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) 86 inline int getCSR() 87 { 88 int result; 89 asm volatile("stmxcsr %0" : "=m" (result)); 90 return result; 91 } 92 93 inline void setCSR(int a) 94 { 95 int temp = a; 96 asm volatile("ldmxcsr %0" : : "m" (temp)); 97 } 98 99#endif 100 101 unsigned int m_savedCSR; 102}; 103 104#else 105// FIXME: add implementations for other architectures and compilers 106class DenormalDisabler { 107public: 108 DenormalDisabler() { } 109 110 // Assume the worst case that other architectures and compilers 111 // need to flush denormals to zero manually. 112 static inline float flushDenormalFloatToZero(float f) 113 { 114 return (fabs(f) < FLT_MIN) ? 0.0f : f; 115 } 116}; 117 118#endif 119 120} // WebCore 121 122#undef HAVE_DENORMAL 123#endif // DenormalDisabler_h 124