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timer.cpp: improve cross-platform & cross-compiler issues relating to precision & period.

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Handle timerlastsample such that we don't throw away time & run slow in certain cases.
Ensure when calculating n, we do the double division first before multiplying for sake of floating point precision.

git-svn-id: https://svn.eduke32.com/eduke32@8009 1a8010ca-5511-0410-912e-c29ae57300e0
This commit is contained in:
pogokeen 2019-08-14 21:42:30 +00:00 committed by Christoph Oelckers
parent 002a52033d
commit 021e1358c7
1 changed files with 6 additions and 3 deletions
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9
source/build/src/timer.cpp
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@ -9,13 +9,15 @@
using namespace std;
using namespace chrono;
EDUKE32_STATIC_ASSERT((steady_clock::period::den/steady_clock::period::num) >= 1000000000);
static time_point<steady_clock> timerlastsample;
static int timerticspersec;
static void(*usertimercallback)(void) = NULL;
int timerGetRate(void) { return timerticspersec; }
uint32_t timerGetTicks(void) { return duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count(); }
uint64_t timerGetTicksU64(void) { return steady_clock::now().time_since_epoch().count(); }
uint64_t timerGetTicksU64(void) { return steady_clock::now().time_since_epoch().count() * steady_clock::period::num; }
uint64_t timerGetFreqU64(void) { return steady_clock::period::den; }
// Returns the time since an unspecified starting time in milliseconds.
@ -35,12 +37,13 @@ int timerInit(int const tickspersecond)
ATTRIBUTE((flatten)) void timerUpdate(void)
{
auto time = steady_clock::now();
int n = (time - timerlastsample).count() * (double)timerticspersec / timerGetFreqU64();
auto elapsedTime = time - timerlastsample;
int n = elapsedTime.count() * ((double)timerticspersec / timerGetFreqU64()) * steady_clock::period::num;
if (n <= 0) return;
totalclock += n;
timerlastsample = time;
timerlastsample += n*nanoseconds(1000000000/timerticspersec);
if (usertimercallback)
for (; n > 0; n--) usertimercallback();