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