[libcxx-commits] [PATCH] D104987: Use GetSystemTimePreciseAsFileTime() if available

[Sizhe Zhao via Phabricator via libcxx-commits]

Prince213 updated this revision to Diff 357706.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D104987/new/

https://reviews.llvm.org/D104987

Files:
  libcxx/src/chrono.cpp


Index: libcxx/src/chrono.cpp
===================================================================
--- libcxx/src/chrono.cpp
+++ libcxx/src/chrono.cpp
@@ -63,6 +63,19 @@
 
 #if defined(_LIBCPP_WIN32API)
 
+#if _WIN32_WINNT < _WIN32_WINNT_WIN8
+
+typedef void(WINAPI* FP)(LPFILETIME);
+
+static FP init_system_clock() {
+  FP fp = (FP)GetProcAddress(GetModuleHandleW(L"kernel32.dll"), "GetSystemTimePreciseAsFileTime");
+  if (nullptr == fp)
+    return GetSystemTimeAsFileTime;
+  return fp;
+}
+
+#endif
+
 static system_clock::time_point __libcpp_system_clock_now() {
   // FILETIME is in 100ns units
   using filetime_duration =
@@ -74,10 +87,11 @@
   static _LIBCPP_CONSTEXPR const seconds nt_to_unix_epoch{11644473600};
 
   FILETIME ft;
-#if _WIN32_WINNT >= _WIN32_WINNT_WIN8 && WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+#if _WIN32_WINNT >= _WIN32_WINNT_WIN8
   GetSystemTimePreciseAsFileTime(&ft);
 #else
-  GetSystemTimeAsFileTime(&ft);
+  static FP fp = init_system_clock();
+  fp(&ft);
 #endif
 
   filetime_duration d{(static_cast<__int64>(ft.dwHighDateTime) << 32) |


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