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comparison: content/media/webaudio/blink/DenormalDisabler.h
content/media/webaudio/blink/DenormalDisabler.h
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| 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 #define _USE_MATH_DEFINES | |
| 29 #include <cmath> | |
| 30 #include <float.h> | |
| 31 | |
| 32 namespace WebCore { | |
| 33 | |
| 34 // Deal with denormals. They can very seriously impact performance on x86. | |
| 35 | |
| 36 // Define HAVE_DENORMAL if we support flushing denormals to zero. | |
| 37 #if defined(XP_WIN) && defined(_MSC_VER) | |
| 38 #define HAVE_DENORMAL | |
| 39 #endif | |
| 40 | |
| 41 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) | |
| 42 #define HAVE_DENORMAL | |
| 43 #endif | |
| 44 | |
| 45 #ifdef HAVE_DENORMAL | |
| 46 class DenormalDisabler { | |
| 47 public: | |
| 48 DenormalDisabler() | |
| 49 : m_savedCSR(0) | |
| 50 { | |
| 51 #if defined(XP_WIN) && defined(_MSC_VER) | |
| 52 // Save the current state, and set mode to flush denormals. | |
| 53 // | |
| 54 // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly | |
| 55 _controlfp_s(&m_savedCSR, 0, 0); | |
| 56 unsigned int unused; | |
| 57 _controlfp_s(&unused, _DN_FLUSH, _MCW_DN); | |
| 58 #else | |
| 59 m_savedCSR = getCSR(); | |
| 60 setCSR(m_savedCSR | 0x8040); | |
| 61 #endif | |
| 62 } | |
| 63 | |
| 64 ~DenormalDisabler() | |
| 65 { | |
| 66 #if defined(XP_WIN) && defined(_MSC_VER) | |
| 67 unsigned int unused; | |
| 68 _controlfp_s(&unused, m_savedCSR, _MCW_DN); | |
| 69 #else | |
| 70 setCSR(m_savedCSR); | |
| 71 #endif | |
| 72 } | |
| 73 | |
| 74 // This is a nop if we can flush denormals to zero in hardware. | |
| 75 static inline float flushDenormalFloatToZero(float f) | |
| 76 { | |
| 77 #if defined(XP_WIN) && defined(_MSC_VER) && _M_IX86_FP | |
| 78 // For systems using x87 instead of sse, there's no hardware support | |
| 79 // to flush denormals automatically. Hence, we need to flush | |
| 80 // denormals to zero manually. | |
| 81 return (fabs(f) < FLT_MIN) ? 0.0f : f; | |
| 82 #else | |
| 83 return f; | |
| 84 #endif | |
| 85 } | |
| 86 private: | |
| 87 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) | |
| 88 inline int getCSR() | |
| 89 { | |
| 90 int result; | |
| 91 asm volatile("stmxcsr %0" : "=m" (result)); | |
| 92 return result; | |
| 93 } | |
| 94 | |
| 95 inline void setCSR(int a) | |
| 96 { | |
| 97 int temp = a; | |
| 98 asm volatile("ldmxcsr %0" : : "m" (temp)); | |
| 99 } | |
| 100 | |
| 101 #endif | |
| 102 | |
| 103 unsigned int m_savedCSR; | |
| 104 }; | |
| 105 | |
| 106 #else | |
| 107 // FIXME: add implementations for other architectures and compilers | |
| 108 class DenormalDisabler { | |
| 109 public: | |
| 110 DenormalDisabler() { } | |
| 111 | |
| 112 // Assume the worst case that other architectures and compilers | |
| 113 // need to flush denormals to zero manually. | |
| 114 static inline float flushDenormalFloatToZero(float f) | |
| 115 { | |
| 116 return (fabs(f) < FLT_MIN) ? 0.0f : f; | |
| 117 } | |
| 118 }; | |
| 119 | |
| 120 #endif | |
| 121 | |
| 122 } // WebCore | |
| 123 | |
| 124 #undef HAVE_DENORMAL | |
| 125 #endif // DenormalDisabler_h |
