Use high-precision clock time on Windows 8 and up.

original commit: 15982a28189454d5b7b3b065db5aac9816781bde

LOG

@@ -320,3 +320,5 @@
   the full buffer (but reporting that it did) in the case of errors from
   write.
     examples/csocket.c, examples/socket.ss
+- use high-precision clock time on Windows 8 and up
+    c/stats.c

c/stats.c

@@ -115,6 +115,10 @@ ptr S_unique_id() {
 
 static __int64 hires_cps = 0;
 
+typedef void (WINAPI *GetSystemTimeAsFileTime_t)(LPFILETIME lpSystemTimeAsFileTime);
+
+static GetSystemTimeAsFileTime_t s_GetSystemTimeAsFileTime = GetSystemTimeAsFileTime;
+
 static void s_gettime(INT typeno, struct timespec *tp) {
   switch (typeno) {
     case time_process: {
@@ -189,7 +193,7 @@ static void s_gettime(INT typeno, struct timespec *tp) {
     case time_utc: {
       FILETIME ft; __int64 total;
 
-      GetSystemTimeAsFileTime(&ft);
+      s_GetSystemTimeAsFileTime(&ft);
       total = ft.dwHighDateTime;
       total <<= 32;
       total |= ft.dwLowDateTime;
@@ -459,5 +463,14 @@ ptr S_realtime(void) {
 /********  initialization  ********/
 
 void S_stats_init() {
+  /* Use GetSystemTimePreciseAsFileTime when available (Windows 8 and later). */
+  HMODULE h = LoadLibrary("kernel32.dll");
+  if (h != NULL) {
+    GetSystemTimeAsFileTime_t proc = (GetSystemTimeAsFileTime_t)GetProcAddress(h, "GetSystemTimePreciseAsFileTime");
+    if (proc != NULL)
+      s_GetSystemTimeAsFileTime = proc;
+    else
+      FreeLibrary(h);
+  }
   s_gettime(time_monotonic, &starting_mono_tp);
 }

release_notes/release_notes.stex

@@ -58,6 +58,11 @@ Online versions of both books can be found at
 %-----------------------------------------------------------------------------
 \section{Functionality Changes}\label{section:functionality}
 
+\subsection{High-precision clock time in Windows 8 and up (9.4.1)}
+
+When running on Windows 8 and up, Chez Scheme uses the high-precision
+clock time function for the current date and time.
+
 \subsection{Printing of non-standard (extended) identifiers (9.4.1)}
 
 Chez Scheme extends the syntax of identifiers as described in the