Query the interrupt timer in Windows without any API calls.

timer.c

#include <inttypes.h>
#include <stdio.h>

static uint64_t get_interrupt_time()
{
	const void* const shared_user_data = (void*)0x7ffe0000;
	const volatile struct {
		uint32_t low;
		uint32_t high1;
		uint32_t high2;
	}* const interrupt_time = (void*)((uint32_t*)shared_user_data + 2);

	union {
		struct {
			uint32_t low;
			uint32_t high;
		} t;
		uint64_t i;
	} icopy;

	do {
		icopy.t.high = interrupt_time->high1;
		icopy.t.low = interrupt_time->low;
	} while (interrupt_time->high2 != icopy.t.high);

	return icopy.i;
}

int main()
{
	uint64_t itime, itime_old, itime_offset, delta;
	unsigned counter = 0;

	itime_offset = get_interrupt_time();
	itime_old = itime_offset;

	for (;;) {
		do itime = get_interrupt_time();
		while (itime <= itime_old);

		delta = itime - itime_old;
		itime_old = itime;
		itime -= itime_offset;

		if (++counter == 32) {
			printf("t=%" PRIu64 ".%07" PRIu64 "s  "
				"d=%" PRIu64 ".%04" PRIu64 "ms                \r",
				itime / UINT64_C(10000000), itime % UINT64_C(10000000),
				delta / UINT64_C(10000), delta % UINT64_C(10000));
			fflush(stdout);

			counter = 0;
		}
	}
}