import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

dom/media/webaudio/blink/DenormalDisabler.h

@@ -0,0 +1,124 @@
+/*
+ * 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 <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)
+#define HAVE_DENORMAL
+#endif
+
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+#define HAVE_DENORMAL
+#endif
+
+#ifdef HAVE_DENORMAL
+class DenormalDisabler {
+public:
+    DenormalDisabler()
+            : m_savedCSR(0)
+    {
+#if defined(XP_WIN) && defined(_MSC_VER)
+        // 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 int unused;
+        _controlfp_s(&unused, _DN_FLUSH, _MCW_DN);
+#else
+        m_savedCSR = getCSR();
+        setCSR(m_savedCSR | 0x8040);
+#endif
+    }
+
+    ~DenormalDisabler()
+    {
+#if defined(XP_WIN) && defined(_MSC_VER)
+        unsigned int unused;
+        _controlfp_s(&unused, m_savedCSR, _MCW_DN);
+#else
+        setCSR(m_savedCSR);
+#endif
+    }
+
+    // This is a nop if we can flush denormals to zero in hardware.
+    static inline float flushDenormalFloatToZero(float f)
+    {
+#if defined(XP_WIN) && defined(_MSC_VER) && _M_IX86_FP
+        // For systems using x87 instead of sse, there's no hardware support
+        // to flush denormals automatically. Hence, we need to flush
+        // denormals to zero manually.
+        return (fabs(f) < FLT_MIN) ? 0.0f : f;
+#else
+        return f;
+#endif
+    }
+private:
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+    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));
+    }
+
+#endif
+
+    unsigned int m_savedCSR;
+};
+
+#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
+
+#undef HAVE_DENORMAL
+#endif // DenormalDisabler_h