//+private
//+build linux
package time

import "core:intrinsics"
import "core:sys/unix"

_get_tsc_frequency :: proc "contextless" () -> (u64, bool) {
	perf_attr := unix.Perf_Event_Attr{}
	perf_attr.type = u32(unix.Perf_Type_Id.Hardware)
	perf_attr.config = u64(unix.Perf_Hardware_Id.Instructions)
	perf_attr.size = size_of(perf_attr)
	perf_attr.flags = {.Disabled, .Exclude_Kernel, .Exclude_HV}
	fd := unix.sys_perf_event_open(&perf_attr, 0, -1, -1, 0)
	if fd == -1 {
		return 0, false
	}
	defer unix.sys_close(fd)

	page_size : uint = 4096
	ret := unix.sys_mmap(nil, page_size, unix.PROT_READ, unix.MAP_SHARED, fd, 0)
	if ret < 0 && ret > -4096 {
		return 0, false
	}
	addr := rawptr(uintptr(ret))
	defer unix.sys_munmap(addr, page_size)

	event_page := (^unix.Perf_Event_mmap_Page)(addr)
	if .User_Time not_in event_page.cap.flags {
		return 0, false
	}

	frequency := u64((u128(1_000_000_000) << u128(event_page.time_shift)) / u128(event_page.time_mult))
	return frequency, true
}