diff options
author | RĂ©mi Verschelde <rverschelde@gmail.com> | 2020-06-11 09:38:44 +0200 |
---|---|---|
committer | GitHub <noreply@github.com> | 2020-06-11 09:38:44 +0200 |
commit | c4dd866a15744fc6df8b7abb8a0af77612d28b2e (patch) | |
tree | 71018e04f4b198153644b1e0fd8a167910789c14 | |
parent | 7217a7edbd6beb265b3232953cbeaa9dcea62414 (diff) | |
parent | db9fa8816056b367a5d97f57c2498241aaef974a (diff) |
Merge pull request #38958 from lawnjelly/time_overflow_4
Fix overflow condition with QueryPerformanceCounter
-rw-r--r-- | platform/uwp/os_uwp.cpp | 21 | ||||
-rw-r--r-- | platform/windows/os_windows.cpp | 21 |
2 files changed, 38 insertions, 4 deletions
diff --git a/platform/uwp/os_uwp.cpp b/platform/uwp/os_uwp.cpp index 7bd67d3726..ee25754704 100644 --- a/platform/uwp/os_uwp.cpp +++ b/platform/uwp/os_uwp.cpp @@ -535,11 +535,28 @@ void OS_UWP::delay_usec(uint32_t p_usec) const { uint64_t OS_UWP::get_ticks_usec() const { uint64_t ticks; - uint64_t time; + // This is the number of clock ticks since start QueryPerformanceCounter((LARGE_INTEGER *)&ticks); + // Divide by frequency to get the time in seconds - time = ticks * 1000000L / ticks_per_second; + // original calculation shown below is subject to overflow + // with high ticks_per_second and a number of days since the last reboot. + // time = ticks * 1000000L / ticks_per_second; + + // we can prevent this by either using 128 bit math + // or separating into a calculation for seconds, and the fraction + uint64_t seconds = ticks / ticks_per_second; + + // compiler will optimize these two into one divide + uint64_t leftover = ticks % ticks_per_second; + + // remainder + uint64_t time = (leftover * 1000000L) / ticks_per_second; + + // seconds + time += seconds * 1000000L; + // Subtract the time at game start to get // the time since the game started time -= ticks_start; diff --git a/platform/windows/os_windows.cpp b/platform/windows/os_windows.cpp index 0dab0c601a..29eabfdde8 100644 --- a/platform/windows/os_windows.cpp +++ b/platform/windows/os_windows.cpp @@ -403,12 +403,29 @@ void OS_Windows::delay_usec(uint32_t p_usec) const { uint64_t OS_Windows::get_ticks_usec() const { uint64_t ticks; - uint64_t time; + // This is the number of clock ticks since start if (!QueryPerformanceCounter((LARGE_INTEGER *)&ticks)) ticks = (UINT64)timeGetTime(); + // Divide by frequency to get the time in seconds - time = ticks * 1000000L / ticks_per_second; + // original calculation shown below is subject to overflow + // with high ticks_per_second and a number of days since the last reboot. + // time = ticks * 1000000L / ticks_per_second; + + // we can prevent this by either using 128 bit math + // or separating into a calculation for seconds, and the fraction + uint64_t seconds = ticks / ticks_per_second; + + // compiler will optimize these two into one divide + uint64_t leftover = ticks % ticks_per_second; + + // remainder + uint64_t time = (leftover * 1000000L) / ticks_per_second; + + // seconds + time += seconds * 1000000L; + // Subtract the time at game start to get // the time since the game started time -= ticks_start; |