1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/content/media/webaudio/blink/DenormalDisabler.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,125 @@
1.4 +/*
1.5 + * Copyright (C) 2011, Google Inc. All rights reserved.
1.6 + *
1.7 + * Redistribution and use in source and binary forms, with or without
1.8 + * modification, are permitted provided that the following conditions
1.9 + * are met:
1.10 + * 1. Redistributions of source code must retain the above copyright
1.11 + * notice, this list of conditions and the following disclaimer.
1.12 + * 2. Redistributions in binary form must reproduce the above copyright
1.13 + * notice, this list of conditions and the following disclaimer in the
1.14 + * documentation and/or other materials provided with the distribution.
1.15 + *
1.16 + * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
1.17 + * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
1.18 + * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
1.19 + * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
1.20 + * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
1.21 + * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
1.22 + * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
1.23 + * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
1.24 + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
1.25 + * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
1.26 + */
1.27 +
1.28 +#ifndef DenormalDisabler_h
1.29 +#define DenormalDisabler_h
1.30 +
1.31 +#define _USE_MATH_DEFINES
1.32 +#include <cmath>
1.33 +#include <float.h>
1.34 +
1.35 +namespace WebCore {
1.36 +
1.37 +// Deal with denormals. They can very seriously impact performance on x86.
1.38 +
1.39 +// Define HAVE_DENORMAL if we support flushing denormals to zero.
1.40 +#if defined(XP_WIN) && defined(_MSC_VER)
1.41 +#define HAVE_DENORMAL
1.42 +#endif
1.43 +
1.44 +#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
1.45 +#define HAVE_DENORMAL
1.46 +#endif
1.47 +
1.48 +#ifdef HAVE_DENORMAL
1.49 +class DenormalDisabler {
1.50 +public:
1.51 + DenormalDisabler()
1.52 + : m_savedCSR(0)
1.53 + {
1.54 +#if defined(XP_WIN) && defined(_MSC_VER)
1.55 + // Save the current state, and set mode to flush denormals.
1.56 + //
1.57 + // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly
1.58 + _controlfp_s(&m_savedCSR, 0, 0);
1.59 + unsigned int unused;
1.60 + _controlfp_s(&unused, _DN_FLUSH, _MCW_DN);
1.61 +#else
1.62 + m_savedCSR = getCSR();
1.63 + setCSR(m_savedCSR | 0x8040);
1.64 +#endif
1.65 + }
1.66 +
1.67 + ~DenormalDisabler()
1.68 + {
1.69 +#if defined(XP_WIN) && defined(_MSC_VER)
1.70 + unsigned int unused;
1.71 + _controlfp_s(&unused, m_savedCSR, _MCW_DN);
1.72 +#else
1.73 + setCSR(m_savedCSR);
1.74 +#endif
1.75 + }
1.76 +
1.77 + // This is a nop if we can flush denormals to zero in hardware.
1.78 + static inline float flushDenormalFloatToZero(float f)
1.79 + {
1.80 +#if defined(XP_WIN) && defined(_MSC_VER) && _M_IX86_FP
1.81 + // For systems using x87 instead of sse, there's no hardware support
1.82 + // to flush denormals automatically. Hence, we need to flush
1.83 + // denormals to zero manually.
1.84 + return (fabs(f) < FLT_MIN) ? 0.0f : f;
1.85 +#else
1.86 + return f;
1.87 +#endif
1.88 + }
1.89 +private:
1.90 +#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
1.91 + inline int getCSR()
1.92 + {
1.93 + int result;
1.94 + asm volatile("stmxcsr %0" : "=m" (result));
1.95 + return result;
1.96 + }
1.97 +
1.98 + inline void setCSR(int a)
1.99 + {
1.100 + int temp = a;
1.101 + asm volatile("ldmxcsr %0" : : "m" (temp));
1.102 + }
1.103 +
1.104 +#endif
1.105 +
1.106 + unsigned int m_savedCSR;
1.107 +};
1.108 +
1.109 +#else
1.110 +// FIXME: add implementations for other architectures and compilers
1.111 +class DenormalDisabler {
1.112 +public:
1.113 + DenormalDisabler() { }
1.114 +
1.115 + // Assume the worst case that other architectures and compilers
1.116 + // need to flush denormals to zero manually.
1.117 + static inline float flushDenormalFloatToZero(float f)
1.118 + {
1.119 + return (fabs(f) < FLT_MIN) ? 0.0f : f;
1.120 + }
1.121 +};
1.122 +
1.123 +#endif
1.124 +
1.125 +} // WebCore
1.126 +
1.127 +#undef HAVE_DENORMAL
1.128 +#endif // DenormalDisabler_h
