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https://github.com/rust-lang/rust.git
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Vadim Chugunov
74 lines
2.4 KiB
Rust
74 lines
2.4 KiB
Rust
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use libc;
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use ops::Sub;
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use time::Duration;
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use sync::{Once, ONCE_INIT};
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const NANOS_PER_SEC: i64 = 1_000_000_000;
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pub struct SteadyTime {
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t: libc::LARGE_INTEGER,
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}
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impl SteadyTime {
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pub fn now() -> SteadyTime {
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let mut t = SteadyTime { t: 0 };
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unsafe { libc::QueryPerformanceCounter(&mut t.t); }
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t
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}
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pub fn ns(&self) -> u64 {
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mul_div_i64(self.t as i64, NANOS_PER_SEC, frequency() as i64) as u64
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}
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}
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fn frequency() -> libc::LARGE_INTEGER {
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static mut FREQUENCY: libc::LARGE_INTEGER = 0;
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static ONCE: Once = ONCE_INIT;
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unsafe {
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ONCE.call_once(|| {
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libc::QueryPerformanceFrequency(&mut FREQUENCY);
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});
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FREQUENCY
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}
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}
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impl<'a> Sub for &'a SteadyTime {
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type Output = Duration;
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fn sub(self, other: &SteadyTime) -> Duration {
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let diff = self.t as i64 - other.t as i64;
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Duration::nanoseconds(mul_div_i64(diff, NANOS_PER_SEC, frequency() as i64))
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}
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}
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// Computes (value*numer)/denom without overflow, as long as both
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// (numer*denom) and the overall result fit into i64 (which is the case
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// for our time conversions).
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fn mul_div_i64(value: i64, numer: i64, denom: i64) -> i64 {
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let q = value / denom;
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let r = value % denom;
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// Decompose value as (value/denom*denom + value%denom),
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// substitute into (value*numer)/denom and simplify.
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// r < denom, so (denom*numer) is the upper bound of (r*numer)
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q * numer + r * numer / denom
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}
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#[test]
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fn test_muldiv() {
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assert_eq!(mul_div_i64( 1_000_000_000_001, 1_000_000_000, 1_000_000), 1_000_000_000_001_000);
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assert_eq!(mul_div_i64(-1_000_000_000_001, 1_000_000_000, 1_000_000), -1_000_000_000_001_000);
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assert_eq!(mul_div_i64(-1_000_000_000_001,-1_000_000_000, 1_000_000), 1_000_000_000_001_000);
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assert_eq!(mul_div_i64( 1_000_000_000_001, 1_000_000_000,-1_000_000), -1_000_000_000_001_000);
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assert_eq!(mul_div_i64( 1_000_000_000_001,-1_000_000_000,-1_000_000), 1_000_000_000_001_000);
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}
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