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diff --git a/third_party/aom/test/register_state_check.h b/third_party/aom/test/register_state_check.h
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+/*
+ * Copyright (c) 2016, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
+#ifndef AOM_TEST_REGISTER_STATE_CHECK_H_
+#define AOM_TEST_REGISTER_STATE_CHECK_H_
+
+#include "third_party/googletest/src/googletest/include/gtest/gtest.h"
+
+#include "config/aom_config.h"
+
+#include "aom/aom_integer.h"
+
+// ASM_REGISTER_STATE_CHECK(asm_function)
+//   Minimally validates the environment pre & post function execution. This
+//   variant should be used with assembly functions which are not expected to
+//   fully restore the system state. See platform implementations of
+//   RegisterStateCheck for details.
+//
+// API_REGISTER_STATE_CHECK(api_function)
+//   Performs all the checks done by ASM_REGISTER_STATE_CHECK() and any
+//   additional checks to ensure the environment is in a consistent state pre &
+//   post function execution. This variant should be used with API functions.
+//   See platform implementations of RegisterStateCheckXXX for details.
+//
+
+#if defined(_WIN64) && ARCH_X86_64
+
+#undef NOMINMAX
+#define NOMINMAX
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <winnt.h>
+
+inline bool operator==(const M128A &lhs, const M128A &rhs) {
+  return (lhs.Low == rhs.Low && lhs.High == rhs.High);
+}
+
+namespace libaom_test {
+
+// Compares the state of xmm[6-15] at construction with their state at
+// destruction. These registers should be preserved by the callee on
+// Windows x64.
+class RegisterStateCheck {
+ public:
+  RegisterStateCheck() { initialized_ = StoreRegisters(&pre_context_); }
+  ~RegisterStateCheck() { Check(); }
+
+ private:
+  static bool StoreRegisters(CONTEXT *const context) {
+    const HANDLE this_thread = GetCurrentThread();
+    EXPECT_TRUE(this_thread != NULL);
+    context->ContextFlags = CONTEXT_FLOATING_POINT;
+    const bool context_saved = GetThreadContext(this_thread, context) == TRUE;
+    EXPECT_TRUE(context_saved) << "GetLastError: " << GetLastError();
+    return context_saved;
+  }
+
+  // Compares the register state. Returns true if the states match.
+  void Check() const {
+    ASSERT_TRUE(initialized_);
+    CONTEXT post_context;
+    ASSERT_TRUE(StoreRegisters(&post_context));
+
+    const M128A *xmm_pre = &pre_context_.Xmm6;
+    const M128A *xmm_post = &post_context.Xmm6;
+    for (int i = 6; i <= 15; ++i) {
+      EXPECT_EQ(*xmm_pre, *xmm_post) << "xmm" << i << " has been modified!";
+      ++xmm_pre;
+      ++xmm_post;
+    }
+  }
+
+  bool initialized_;
+  CONTEXT pre_context_;
+};
+
+#define ASM_REGISTER_STATE_CHECK(statement)    \
+  do {                                         \
+    libaom_test::RegisterStateCheck reg_check; \
+    statement;                                 \
+  } while (false)
+
+}  // namespace libaom_test
+
+#else
+
+namespace libaom_test {
+
+class RegisterStateCheck {};
+#define ASM_REGISTER_STATE_CHECK(statement) statement
+
+}  // namespace libaom_test
+
+#endif  // _WIN64 && ARCH_X86_64
+
+#if ARCH_X86 || ARCH_X86_64
+#if defined(__GNUC__)
+
+namespace libaom_test {
+
+// Checks the FPU tag word pre/post execution to ensure emms has been called.
+class RegisterStateCheckMMX {
+ public:
+  RegisterStateCheckMMX() {
+    __asm__ volatile("fstenv %0" : "=rm"(pre_fpu_env_));
+  }
+  ~RegisterStateCheckMMX() { Check(); }
+
+ private:
+  // Checks the FPU tag word pre/post execution, returning false if not cleared
+  // to 0xffff.
+  void Check() const {
+    EXPECT_EQ(0xffff, pre_fpu_env_[4])
+        << "FPU was in an inconsistent state prior to call";
+
+    uint16_t post_fpu_env[14];
+    __asm__ volatile("fstenv %0" : "=rm"(post_fpu_env));
+    EXPECT_EQ(0xffff, post_fpu_env[4])
+        << "FPU was left in an inconsistent state after call";
+  }
+
+  uint16_t pre_fpu_env_[14];
+};
+
+#define API_REGISTER_STATE_CHECK(statement)       \
+  do {                                            \
+    libaom_test::RegisterStateCheckMMX reg_check; \
+    ASM_REGISTER_STATE_CHECK(statement);          \
+  } while (false)
+
+}  // namespace libaom_test
+
+#endif  // __GNUC__
+#endif  // ARCH_X86 || ARCH_X86_64
+
+#ifndef API_REGISTER_STATE_CHECK
+#define API_REGISTER_STATE_CHECK ASM_REGISTER_STATE_CHECK
+#endif
+
+#endif  // AOM_TEST_REGISTER_STATE_CHECK_H_