From 3a895e313b91bd8b23bab81d45efce63ca47cde7 Mon Sep 17 00:00:00 2001
From: Bruno Haible <bruno@clisp.org>
Date: Sun, 27 Oct 2019 22:51:43 +0100
Subject: [PATCH] Fix compilation error on MSVC.

Based on code that I wrote for gnulib.
---
 src/base/random/cl_random_from.cc | 18 +++++++++----
 src/timing/cl_t_current.cc        | 43 +++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/src/base/random/cl_random_from.cc b/src/base/random/cl_random_from.cc
index 3614cc3..d187f47 100644
--- a/src/base/random/cl_random_from.cc
+++ b/src/base/random/cl_random_from.cc
@@ -62,15 +62,23 @@ inline uint32 get_seed (void)
 #endif
 
 #elif defined(_WIN32) && !defined(__CYGWIN__)
-#include <sys/time.h>
-#include <sys/timeb.h>
+
+/* <windows.h> included above. */
 
 namespace cln {
 inline uint32 get_seed (void)
 {
-	struct timeb timebuf;
-	ftime(&timebuf);
-	return highlow32(timebuf.time, (long)(timebuf.millitm)*1000);
+	FILETIME current_time;
+
+	GetSystemTimeAsFileTime (&current_time);
+
+	/* Convert from FILETIME to 'struct timeval'.  */
+	/* FILETIME: <https://docs.microsoft.com/en-us/windows/desktop/api/minwinbase/ns-minwinbase-filetime> */
+	ULONGLONG since_1601 =
+		((ULONGLONG) current_time.dwHighDateTime << 32)
+		| (ULONGLONG) current_time.dwLowDateTime;
+	/* Divide by 20 ms, and take the low-order 32 bits. */
+	return (ULONG) (since_1601 / 2000000);
 }
 }  // namespace cln
 
diff --git a/src/timing/cl_t_current.cc b/src/timing/cl_t_current.cc
index aa5d3b1..6800e39 100644
--- a/src/timing/cl_t_current.cc
+++ b/src/timing/cl_t_current.cc
@@ -1,5 +1,9 @@
 // cl_current_time().
 
+#if defined(_WIN32) && !defined(__CYGWIN__)
+#include <windows.h> // For GetSystemTimeAsFileTime(), must be included first, sorry.
+#endif
+
 // General includes.
 #include "base/cl_sysdep.h"
 
@@ -19,6 +23,8 @@
   #else
     extern "C" int gettimeofday (struct timeval * tp, GETTIMEOFDAY_TZP_T tzp);
   #endif
+#elif defined(_WIN32) && !defined(__CYGWIN__)
+  /* <windows.h> included above. */
 #else
   #include <ctime>
 #endif
@@ -42,6 +48,43 @@ const cl_timespec cl_current_time ()
 	return cl_timespec(tv.tv_sec,
 			   tv.tv_usec * (1000000000/1000000)
 			  );
+#elif defined(_WIN32) && !defined(__CYGWIN__)
+
+	/* GetSystemTimePreciseAsFileTime was introduced only in Windows 8.  */
+	typedef void (WINAPI * GetSystemTimePreciseAsFileTimeFuncType) (FILETIME *lpTime);
+	static GetSystemTimePreciseAsFileTimeFuncType GetSystemTimePreciseAsFileTimeFunc = NULL;
+	static BOOL initialized = FALSE;
+
+	if (!initialized) {
+		HMODULE kernel32 = LoadLibrary ("kernel32.dll");
+		if (kernel32 != NULL) {
+			GetSystemTimePreciseAsFileTimeFunc =
+				(GetSystemTimePreciseAsFileTimeFuncType) (void *) GetProcAddress (kernel32, "GetSystemTimePreciseAsFileTime");
+		}
+		initialized = TRUE;
+	}
+
+	FILETIME current_time;
+
+	if (GetSystemTimePreciseAsFileTimeFunc != NULL)
+		GetSystemTimePreciseAsFileTimeFunc (&current_time);
+	else
+		GetSystemTimeAsFileTime (&current_time);
+
+	/* Convert from FILETIME to 'struct timeval'.  */
+	/* FILETIME: <https://docs.microsoft.com/en-us/windows/desktop/api/minwinbase/ns-minwinbase-filetime> */
+	ULONGLONG since_1601 =
+		((ULONGLONG) current_time.dwHighDateTime << 32)
+		| (ULONGLONG) current_time.dwLowDateTime;
+	/* Between 1601-01-01 and 1970-01-01 there were 280 normal years and 89 leap
+	   years, in total 134774 days.  */
+	ULONGLONG since_1970 =
+		since_1601 - (ULONGLONG) 134774 * (ULONGLONG) 86400 * (ULONGLONG) 10000000;
+	ULONGLONG microseconds_since_1970 = since_1970 / (ULONGLONG) 10;
+	return cl_timespec(microseconds_since_1970 / (ULONGLONG) 1000000,
+			   (microseconds_since_1970 % (ULONGLONG) 1000000) * (1000000000/1000000)
+			  );
+
 #else
 	return cl_timespec(time(NULL),0);
 #endif
-- 
2.49.0