Commit 1fb0f13a authored by Simon Marlow's avatar Simon Marlow

Win32 getProcessElapsedTime: use a higher-resolution time source

QueryPerformanceCounter() on Windows gives much better resolution than
parent a8dc46dc
......@@ -69,12 +69,36 @@ getProcessCPUTime(void)
return fileTimeToTicks(userTime);
// getProcessElapsedTime relies on QueryPerformanceFrequency
// which should be available on any Windows computer thay you
// would want to run Haskell on. Satnam Singh, 5 July 2010.
FILETIME system_time;
return fileTimeToTicks(system_time);
// frequency represents the number of ticks per second
// used by the QueryPerformanceFrequency implementaiton
// and is represented by a 64-bit union type initially set to 0
// and updated just once (hence use of static).
static LARGE_INTEGER frequency = {.QuadPart = 0} ;
// system_time is a 64-bit union type used to represent the
// tick count returned by QueryPerformanceCounter
LARGE_INTEGER system_time ;
// If this is the first time we are calling getProcessElapsedTime
// then record the ticks per second used by QueryPerformanceCounter
if (frequency.QuadPart == 0) {
// Get the tick count.
QueryPerformanceCounter(&system_time) ;
// Return the tick count as a millisecond value.
// Using double to compute the intermediate value, because a 64-bit
// int would overflow when multiplied by TICKS_PER_SECOND in about 81 days.
return (Ticks)((TICKS_PER_SECOND * (double)system_time.QuadPart) / (double)frequency.QuadPart) ;
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