use time::Duration;
use sync::{Once, ONCE_INIT};
+const NANOS_PER_SEC: i64 = 1_000_000_000;
+
pub struct SteadyTime {
t: libc::LARGE_INTEGER,
}
}
pub fn ns(&self) -> u64 {
- self.t as u64 * 1_000_000_000 / frequency() as u64
+ mul_div_i64(self.t as i64, NANOS_PER_SEC, frequency() as i64) as u64
}
}
fn sub(self, other: &SteadyTime) -> Duration {
let diff = self.t as i64 - other.t as i64;
- Duration::microseconds(diff * 1_000_000 / frequency() as i64)
+ Duration::nanoseconds(mul_div_i64(diff, NANOS_PER_SEC, frequency() as i64))
}
}
+
+// 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
+}
+
+#[test]
+fn test_muldiv() {
+ assert_eq!(mul_div_i64( 1_000_000_000_001, 1_000_000_000, 1_000_000), 1_000_000_000_001_000);
+ assert_eq!(mul_div_i64(-1_000_000_000_001, 1_000_000_000, 1_000_000), -1_000_000_000_001_000);
+ assert_eq!(mul_div_i64(-1_000_000_000_001,-1_000_000_000, 1_000_000), 1_000_000_000_001_000);
+ assert_eq!(mul_div_i64( 1_000_000_000_001, 1_000_000_000,-1_000_000), -1_000_000_000_001_000);
+ assert_eq!(mul_div_i64( 1_000_000_000_001,-1_000_000_000,-1_000_000), 1_000_000_000_001_000);
+}