win32: swap GetTickCount64() for more precise QueryPerformanceCounters()

Author: bradh352

src/lib/ares__timeval.c

@@ -30,11 +30,24 @@
 
 void ares__tvnow(ares_timeval_t *now)
 {
-  /* GetTickCount64() is available on Windows Vista and higher */
-  ULONGLONG      milliseconds = GetTickCount64();
+  /* QueryPerformanceCounters() has been around since Windows 2000, though
+   * significant fixes were made in later versions.  Documentation states
+   * 1 microsecond or better resolution with a rollover not less than 100 years.
+   * This differs from GetTickCount{64}() which has a resolution between 10 and
+   * 16 ms. */
+  LARGE_INTEGER freq;
+  LARGE_INTEGER current;
 
-  now->sec  = (ares_int64_t)milliseconds / 1000;
-  now->usec = (unsigned int)(milliseconds % 1000) * 1000;
+  /* Not sure how long it takes to get the frequency, I see it recommended to
+   * cache it */
+  QueryPerformanceFrequency(&freq);
+  QueryPerformanceCounter(&current);
+
+  now->sec = current.QuadPart / freq.QuadPart;
+  /* We want to prevent overflows so we get the remainder, then multiply to
+   * microseconds before dividing */
+  now->usec = (unsigned int)(((current.QuadPart % freq.QuadPart) * 1000000) /
+              freq.QuadPart);
 }
 
 #elif defined(HAVE_CLOCK_GETTIME_MONOTONIC)