vm: more accurate sample timing on windows

diff --git a/vm/os-windows.cpp b/vm/os-windows.cpp
index 2ab696715c17238fe88649aa164ca1052a441390..978cbc7bed8e4836744b2b90745bbfbdd6469338 100755 (executable)
--- a/vm/os-windows.cpp
+++ b/vm/os-windows.cpp
@@ -306,19 +306,19 @@ void factor_vm::sampler_thread_loop()
        LARGE_INTEGER counter, new_counter, units_per_second;
 
        assert(QueryPerformanceFrequency(&units_per_second));
-       long long units_per_sample =
-               units_per_second.QuadPart / FACTOR_PROFILE_SAMPLES_PER_SECOND;
 
        assert(QueryPerformanceCounter(&counter));
+       counter.QuadPart *= FACTOR_PROFILE_SAMPLES_PER_SECOND;
        while (FACTOR_MEMORY_BARRIER(), sampling_profiler_p)
        {
                SwitchToThread();
                assert(QueryPerformanceCounter(&new_counter));
+               new_counter.QuadPart *= FACTOR_PROFILE_SAMPLES_PER_SECOND;
                cell samples = 0;
-               while (new_counter.QuadPart - counter.QuadPart > units_per_sample) {
+               while (new_counter.QuadPart - counter.QuadPart > units_per_second.QuadPart) {
                        // We would have to suspend the thread to sample the PC
                        ++samples;
-                       counter.QuadPart += units_per_sample;
+                       counter.QuadPart += units_per_second.QuadPart;
                }
                if (samples > 0)
                        enqueue_safepoint_sample(samples, 0, false);