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
14  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16  * ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE
17  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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24  */
25 
26 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DENORMAL_DISABLER_H_
27 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DENORMAL_DISABLER_H_
28 
29 #include <float.h>
30 #include "build/build_config.h"
31 #include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
32 #include "third_party/blink/renderer/platform/wtf/math_extras.h"
33 
34 namespace blink {
35 
36 // Deal with denormals. They can very seriously impact performance on x86.
37 
38 // Define HAVE_DENORMAL if we support flushing denormals to zero.
39 
40 #if defined(OS_WIN) && defined(COMPILER_MSVC)
41 // Windows compiled using MSVC with SSE2
42 #define HAVE_DENORMAL 1
43 #endif
44 
45 #if defined(COMPILER_GCC) && defined(ARCH_CPU_X86_FAMILY)
46 // X86 chips can flush denormals
47 #define HAVE_DENORMAL 1
48 #endif
49 
50 #if defined(ARCH_CPU_ARM_FAMILY)
51 #define HAVE_DENORMAL 1
52 #endif
53 
54 #if defined(HAVE_DENORMAL)
55 class DenormalDisabler {
56   DISALLOW_NEW();
57 
58  public:
DenormalDisabler()59   DenormalDisabler() : saved_csr_(0) { DisableDenormals(); }
60 
~DenormalDisabler()61   ~DenormalDisabler() { RestoreState(); }
62 
63   // This is a nop if we can flush denormals to zero in hardware.
FlushDenormalFloatToZero(float f)64   static inline float FlushDenormalFloatToZero(float f) { return f; }
65 
66  private:
67   unsigned saved_csr_;
68 
69 #if defined(COMPILER_GCC) && defined(ARCH_CPU_X86_FAMILY)
DisableDenormals()70   inline void DisableDenormals() {
71     saved_csr_ = GetCSR();
72     SetCSR(saved_csr_ | 0x8040);
73   }
74 
RestoreState()75   inline void RestoreState() { SetCSR(saved_csr_); }
76 
GetCSR()77   inline int GetCSR() {
78     int result;
79     asm volatile("stmxcsr %0" : "=m"(result));
80     return result;
81   }
82 
SetCSR(int a)83   inline void SetCSR(int a) {
84     int temp = a;
85     asm volatile("ldmxcsr %0" : : "m"(temp));
86   }
87 
88 #elif defined(OS_WIN) && defined(COMPILER_MSVC)
DisableDenormals()89   inline void DisableDenormals() {
90     // Save the current state, and set mode to flush denormals.
91     //
92     // http://stackoverflow.com/questions/637175/possible-bug-in-controlfp-s-may-not-restore-control-word-correctly
93     _controlfp_s(&saved_csr_, 0, 0);
94     unsigned unused;
95     _controlfp_s(&unused, _DN_FLUSH, _MCW_DN);
96   }
97 
RestoreState()98   inline void RestoreState() {
99     unsigned unused;
100     _controlfp_s(&unused, saved_csr_, _MCW_DN);
101   }
102 #elif defined(ARCH_CPU_ARM_FAMILY)
DisableDenormals()103   inline void DisableDenormals() {
104     saved_csr_ = GetStatusWord();
105     // Bit 24 is the flush-to-zero mode control bit. Setting it to 1 flushes
106     // denormals to 0.
107     SetStatusWord(saved_csr_ | (1 << 24));
108   }
109 
RestoreState()110   inline void RestoreState() { SetStatusWord(saved_csr_); }
111 
GetStatusWord()112   inline int GetStatusWord() {
113     int result;
114 #if defined(ARCH_CPU_ARM64)
115     asm volatile("mrs %x[result], FPCR" : [result] "=r"(result));
116 #else
117     asm volatile("vmrs %[result], FPSCR" : [result] "=r"(result));
118 #endif
119     return result;
120   }
121 
SetStatusWord(int a)122   inline void SetStatusWord(int a) {
123 #if defined(ARCH_CPU_ARM64)
124     asm volatile("msr FPCR, %x[src]" : : [src] "r"(a));
125 #else
126     asm volatile("vmsr FPSCR, %[src]" : : [src] "r"(a));
127 #endif
128   }
129 
130 #endif
131 };
132 
133 #else
134 // FIXME: add implementations for other architectures and compilers
135 class DenormalDisabler {
136   STACK_ALLOCATED();
137 
138  public:
139   DenormalDisabler() {}
140 
141   // Assume the worst case that other architectures and compilers
142   // need to flush denormals to zero manually.
143   static inline float FlushDenormalFloatToZero(float f) {
144     return (fabs(f) < FLT_MIN) ? 0.0f : f;
145   }
146 };
147 
148 #endif
149 
150 }  // namespace blink
151 
152 #undef HAVE_DENORMAL
153 #endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DENORMAL_DISABLER_H_
154