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/*
* 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 "wtf/Allocator.h"
#include "wtf/CPU.h"
#include "wtf/MathExtras.h"
#include <float.h>
namespace blink {
// Deal with denormals. They can very seriously impact performance on x86.
// Define HAVE_DENORMAL if we support flushing denormals to zero.
#if OS(WIN) && COMPILER(MSVC)
// Windows compiled using MSVC with SSE2
#define HAVE_DENORMAL 1
#endif
#if COMPILER(GCC) && (CPU(X86) || CPU(X86_64))
// X86 chips can flush denormals
#define HAVE_DENORMAL 1
#endif
#if CPU(ARM) || CPU(ARM64)
#define HAVE_DENORMAL 1
#endif
#if HAVE(DENORMAL)
class DenormalDisabler {
DISALLOW_NEW();
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 COMPILER(GCC) && (CPU(X86) || CPU(X86_64))
inline void disableDenormals() {
m_savedCSR = getCSR();
setCSR(m_savedCSR | 0x8040);
}
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 OS(WIN) && COMPILER(MSVC)
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 CPU(ARM) || CPU(ARM64)
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 CPU(ARM64)
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 CPU(ARM64)
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 blink
#undef HAVE_DENORMAL
#endif // DenormalDisabler_h
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