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Diffstat (limited to 'dom/media/webaudio/blink/DenormalDisabler.h')
| -rw-r--r-- | dom/media/webaudio/blink/DenormalDisabler.h | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/dom/media/webaudio/blink/DenormalDisabler.h b/dom/media/webaudio/blink/DenormalDisabler.h new file mode 100644 index 0000000000..646482b74f --- /dev/null +++ b/dom/media/webaudio/blink/DenormalDisabler.h @@ -0,0 +1,170 @@ +/* + * Copyright (C) 2011, Google Inc. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED + * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE + * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR + * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR + * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER + * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + */ + +#ifndef DenormalDisabler_h +#define DenormalDisabler_h + +#include <cmath> +#include <cinttypes> +#include <cstring> +#include <float.h> + +namespace WebCore { + +// Deal with denormals. They can very seriously impact performance on x86. + +// Define HAVE_DENORMAL if we support flushing denormals to zero. + +#if defined(XP_WIN) && defined(_MSC_VER) +// Windows compiled using MSVC with SSE2 +# define HAVE_DENORMAL 1 +#endif + +#if defined(__GNUC__) && defined(__SSE__) +# define HAVE_DENORMAL 1 +#endif + +#if defined(__arm__) || defined(__aarch64__) +# define HAVE_DENORMAL 1 +#endif + +#ifdef HAVE_DENORMAL +class DenormalDisabler { + public: + DenormalDisabler() : m_savedCSR(0) { disableDenormals(); } + + ~DenormalDisabler() { restoreState(); } + + // This is a nop if we can flush denormals to zero in hardware. + static inline float flushDenormalFloatToZero(float f) { return f; } + + private: + unsigned m_savedCSR; + +# if defined(__GNUC__) && defined(__SSE__) + static inline bool isDAZSupported() { +# if defined(__x86_64__) + return true; +# else + static bool s_isInited = false; + static bool s_isSupported = false; + if (s_isInited) { + return s_isSupported; + } + + struct fxsaveResult { + uint8_t before[28]; + uint32_t CSRMask; + uint8_t after[480]; + } __attribute__((aligned(16))); + + fxsaveResult registerData; + memset(®isterData, 0, sizeof(fxsaveResult)); + asm volatile("fxsave %0" : "=m"(registerData)); + s_isSupported = registerData.CSRMask & 0x0040; + s_isInited = true; + return s_isSupported; +# endif + } + + inline void disableDenormals() { + m_savedCSR = getCSR(); + setCSR(m_savedCSR | (isDAZSupported() ? 0x8040 : 0x8000)); + } + + inline void restoreState() { setCSR(m_savedCSR); } + + inline int getCSR() { + int result; + asm volatile("stmxcsr %0" : "=m"(result)); + return result; + } + + inline void setCSR(int a) { + int temp = a; + asm volatile("ldmxcsr %0" : : "m"(temp)); + } + +# elif defined(XP_WIN) && defined(_MSC_VER) + inline void disableDenormals() { + // Save the current state, and set mode to flush denormals. + // + // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly + _controlfp_s(&m_savedCSR, 0, 0); + unsigned unused; + _controlfp_s(&unused, _DN_FLUSH, _MCW_DN); + } + + inline void restoreState() { + unsigned unused; + _controlfp_s(&unused, m_savedCSR, _MCW_DN); + } +# elif defined(__arm__) || defined(__aarch64__) + inline void disableDenormals() { + m_savedCSR = getStatusWord(); + // Bit 24 is the flush-to-zero mode control bit. Setting it to 1 flushes + // denormals to 0. + setStatusWord(m_savedCSR | (1 << 24)); + } + + inline void restoreState() { setStatusWord(m_savedCSR); } + + inline int getStatusWord() { + int result; +# if defined(__aarch64__) + asm volatile("mrs %x[result], FPCR" : [result] "=r"(result)); +# else + asm volatile("vmrs %[result], FPSCR" : [result] "=r"(result)); +# endif + return result; + } + + inline void setStatusWord(int a) { +# if defined(__aarch64__) + asm volatile("msr FPCR, %x[src]" : : [src] "r"(a)); +# else + asm volatile("vmsr FPSCR, %[src]" : : [src] "r"(a)); +# endif + } + +# endif +}; + +#else +// FIXME: add implementations for other architectures and compilers +class DenormalDisabler { + public: + DenormalDisabler() {} + + // Assume the worst case that other architectures and compilers + // need to flush denormals to zero manually. + static inline float flushDenormalFloatToZero(float f) { + return (fabs(f) < FLT_MIN) ? 0.0f : f; + } +}; + +#endif + +} // namespace WebCore +#endif // DenormalDisabler_h |