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//! Timestamp implementation for Windows based on `QueryPerformanceCounter`
use std::mem;
use std::sync::OnceLock;
use winapi::um::profileapi::{QueryPerformanceCounter, QueryPerformanceFrequency};
use winapi::um::winnt::LARGE_INTEGER;
fn i64_to_large_integer(i: i64) -> LARGE_INTEGER {
unsafe {
let mut large_integer: LARGE_INTEGER = mem::zeroed();
*large_integer.QuadPart_mut() = i;
large_integer
}
}
fn large_integer_to_i64(l: LARGE_INTEGER) -> i64 {
unsafe { *l.QuadPart() }
}
fn frequency() -> i64 {
static FREQUENCY: OnceLock<i64> = OnceLock::new();
*FREQUENCY.get_or_init(|| unsafe {
let mut l = i64_to_large_integer(0);
QueryPerformanceFrequency(&mut l);
large_integer_to_i64(l)
})
}
// Computes (value*numer)/denom without overflow, as long as both
// (numer*denom) and the overall result fit into i64 (which is the case
// for our time conversions).
fn mul_div_i64(value: i64, numer: i64, denom: i64) -> i64 {
let q = value / denom;
let r = value % denom;
// Decompose value as (value/denom*denom + value%denom),
// substitute into (value*numer)/denom and simplify.
// r < denom, so (denom*numer) is the upper bound of (r*numer)
q * numer + r * numer / denom
}
/// The time based on [`QueryPerformanceCounter`].
/// This includes the suspend time.
///
/// [QueryPerformanceCounter]: https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter
pub fn now_including_suspend() -> u64 {
let mut ticks = i64_to_large_integer(0);
unsafe {
assert!(QueryPerformanceCounter(&mut ticks) == 1);
}
mul_div_i64(large_integer_to_i64(ticks), 1000000000, frequency()) as u64
}