shithub: ft²

Info  •  Files  •  Log  •  Branches

HPC timer changes

--- a/src/ft2_hpc.c

+++ b/src/ft2_hpc.c

@@ -1,5 +1,13 @@

 /*

-** Hardware Performance Counter delay routines

+** Hardware Performance Counter delay routines by 8bitbubsy.

+**

+** These are by no means well written, and are made for specific

+** usage cases. There may be soome hackish design choices here.

+**

+** NOTE: hpc_SetDurationInHz() has quite a bit of overhead, so it's

+**       recommended to have one hpcFreq_t counter for each delay value,

+**       then call hpc_SetDurationInHz()/hpc_SetDurationInMs() on program

+**       init instead of every time you want to delay.

 */

 #ifdef _WIN32

@@ -13,7 +21,7 @@

 #include <stdbool.h>

 #include "ft2_hpc.h"

-#define FRAC_BITS 63

+#define FRAC_BITS 63 /* leaves one bit for frac overflow test */

 #define FRAC_SCALE (1ULL << FRAC_BITS)

 #define FRAC_MASK (FRAC_SCALE-1)

@@ -31,7 +39,7 @@

 static void (*usleep)(int32_t usec);

-static void usleepGood(int32_t usec)

+static void usleepAcceptable(int32_t usec)

 {

 	LARGE_INTEGER delayInterval;

@@ -51,7 +59,7 @@

 static void windowsSetupUsleep(void)

 {

 	NtDelayExecution = (NTSTATUS (__stdcall *)(BOOL, PLARGE_INTEGER))GetProcAddress(GetModuleHandle("ntdll.dll"), "NtDelayExecution");

-	usleep = (NtDelayExecution != NULL) ? usleepGood : usleepPoor;

+	usleep = (NtDelayExecution != NULL) ? usleepAcceptable : usleepPoor;

 	NtQueryTimerResolution = (NTSTATUS (__stdcall *)(PULONG, PULONG, PULONG))GetProcAddress(GetModuleHandle("ntdll.dll"), "NtQueryTimerResolution");

 	NtSetTimerResolution = (NTSTATUS (__stdcall *)(ULONG, BOOLEAN, PULONG))GetProcAddress(GetModuleHandle("ntdll.dll"), "NtSetTimerResolution");

@@ -92,15 +100,36 @@

 	return ((uint64_t)resultHi << 32) | resultLo;

 }

-void hpc_SetDurationInHz(hpc_t *hpc, uint32_t hz)

+void hpc_SetDurationInHz(hpc_t *hpc, double dHz) // dHz = max 8191.999inf Hz (0.12ms)

 {

+#define BITS_IN_UINT32 32

+

+	/* 19 = Good compensation between fraction bits and max integer size.

+	** Non-realtime OSes probably can't do a thread delay with such a

+	** high precision (0.12ms) anyway.

+	*/

+#define INPUT_FRAC_BITS 19

+#define INPUT_FRAC_SCALE (1UL << INPUT_FRAC_BITS)

+#define INPUT_INT_MAX ((1UL << (BITS_IN_UINT32-INPUT_FRAC_BITS))-1)

+

+	if (dHz > INPUT_INT_MAX)

+		dHz = INPUT_INT_MAX;

+

+	const uint32_t fpHz = (uint32_t)((dHz * INPUT_FRAC_SCALE) + 0.5);

+

 	// set 64:63fp value

-	hpc->durationInt = hpcFreq.freq64 / hz;

-	hpc->durationFrac = getFrac64FromU64DivU32(hpcFreq.freq64, hz) >> 1;

+	const uint64_t fpFreq64 = hpcFreq.freq64 << INPUT_FRAC_BITS;

+	hpc->durationInt = fpFreq64 / fpHz;

+	hpc->durationFrac = getFrac64FromU64DivU32(fpFreq64, fpHz) >> 1; // 64 -> 63 bits (1 bit for frac overflow test)

-	hpc->resetFrame = hz * (60 * 30); // reset counters every half an hour

+	hpc->resetFrame = ((uint64_t)fpHz * (60 * 30)) / INPUT_FRAC_SCALE; // reset counters every half an hour

 }

+void hpc_SetDurationInMs(hpc_t *hpc, double dMs) // dMs = minimum 0.12208521548 ms

+{

+	hpc_SetDurationInHz(hpc, 1000.0 / dMs);

+}

+

 void hpc_ResetCounters(hpc_t *hpc)

 {

 	hpc->endTimeInt = SDL_GetPerformanceCounter() + hpc->durationInt;

@@ -152,7 +181,7 @@

 	/* The counter ("endTimeInt") can accumulate major errors after a couple of hours,

 	** since each frame is not happening at perfect intervals.

 	** To fix this, reset the counter's int & frac once every half an hour. We should only

-	** get up to one frame of stutter while they are resetting, then it's back to normal.

+	** get up to one frame of jitter while they are resetting, then it's back to normal.

 	*/

 	hpc->frameCounter++;

 	if (hpc->frameCounter >= hpc->resetFrame)

--- a/src/ft2_hpc.h

+++ b/src/ft2_hpc.h

@@ -20,7 +20,8 @@

 extern hpcFreq_t hpcFreq;

 void hpc_Init(void);

-void hpc_SetDurationInHz(hpc_t *hpc, uint32_t dHz);

+void hpc_SetDurationInHz(hpc_t *hpc, double dHz); // dHz = max 8191.999inf Hz (0.12ms)

+void hpc_SetDurationInMs(hpc_t *hpc, double dMs); // dMs = minimum 0.12208521548 ms

 void hpc_ResetCounters(hpc_t *hpc);

 void hpc_Wait(hpc_t *hpc);