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 30 namespace 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 44 class DenormalDisabler { 45 public: 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 } 84 private: 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 106 class DenormalDisabler { 107 public: 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
