timer.h

#ifndef timer_H__
#define timer_H__
#include <stdint.h>

#if __linux__ != 0
#include <time.h>

static uint64_t timer_ns() {
#if defined(CLOCK_MONOTONIC_RAW)
	const clockid_t clockid = CLOCK_MONOTONIC_RAW;

#else
	const clockid_t clockid = CLOCK_MONOTONIC;

#endif
	timespec t;
	clock_gettime(clockid, &t);

	return 1000000000ULL * t.tv_sec + t.tv_nsec;
}

#elif _WIN64 != 0
#define NOMINMAX
#include <Windows.h>

static struct TimerBase {
	LARGE_INTEGER freq;
	TimerBase() { QueryPerformanceFrequency(&freq); }
} timerBase;

// the order of global initialisaitons is non-deterministic, do
// not use this routine in the ctors of globally-scoped objects
static uint64_t timer_ns() {
	LARGE_INTEGER t;
	QueryPerformanceCounter(&t);

	return 1000000000ULL * t.QuadPart / timerBase.freq.QuadPart;
}

#elif __APPLE__ != 0
#include <mach/mach_time.h>

static struct TimerBase {
	mach_timebase_info_data_t tb;
	TimerBase() { mach_timebase_info(&tb); }
} timerBase;

// the order of global initialisaitons is non-deterministic, do
// not use this routine in the ctors of globally-scoped objects
static uint64_t timer_ns() {
	const uint64_t t = mach_absolute_time();
	return t * timerBase.tb.numer / timerBase.tb.denom;
}

#endif
#endif // timer_H__