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Merge pull request #38958 from lawnjelly/time_overflow_4 

Fix overflow condition with QueryPerformanceCounter
This commit is contained in:
Rémi Verschelde 2020-06-11 09:38:44 +02:00 committed by GitHub
parent 7217a7edbd db9fa88160
commit c4dd866a15
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 38 additions and 4 deletions
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21
platform/uwp/os_uwp.cpp
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@ -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;

21
platform/windows/os_windows.cpp
View File

@ -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;