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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 <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(&registerData, 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