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    // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Platform-independent platform abstraction
    //!
    //! This is the platform-independent portion of the standard library's
    //! platform abstraction layer, whereas `std::sys` is the
    //! platform-specific portion.
    //!
    //! The relationship between `std::sys_common`, `std::sys` and the
    //! rest of `std` is complex, with dependencies going in all
    //! directions: `std` depending on `sys_common`, `sys_common`
    //! depending on `sys`, and `sys` depending on `sys_common` and `std`.
    //! Ideally `sys_common` would be split into two and the dependencies
    //! between them all would form a dag, facilitating the extraction of
    //! `std::sys` from the standard library.

    #![allow(missing_docs)]

    use sync::Once;
    use sys;

    pub mod at_exit_imp;
    #[cfg(any(not(cargobuild), feature = "backtrace"))]
    pub mod backtrace;
    pub mod condvar;
    pub mod io;
    pub mod memchr;
    pub mod mutex;
    pub mod poison;
    pub mod remutex;
    pub mod rwlock;
    pub mod thread;
    pub mod thread_info;
    pub mod thread_local;
    pub mod util;
    pub mod wtf8;

    #[cfg(target_os = "redox")]
    pub use sys::net;

    #[cfg(not(target_os = "redox"))]
    pub mod net;

    #[cfg(any(not(cargobuild), feature = "backtrace"))]
    #[cfg(any(all(unix, not(any(target_os = "macos", target_os = "ios", target_os = "emscripten"))),
              all(windows, target_env = "gnu")))]
    pub mod gnu;

    // common error constructors

    /// A trait for viewing representations from std types
    #[doc(hidden)]
    pub trait AsInner<Inner: ?Sized> {
        fn as_inner(&self) -> &Inner;
    }

    /// A trait for viewing representations from std types
    #[doc(hidden)]
    pub trait AsInnerMut<Inner: ?Sized> {
        fn as_inner_mut(&mut self) -> &mut Inner;
    }

    /// A trait for extracting representations from std types
    #[doc(hidden)]
    pub trait IntoInner<Inner> {
        fn into_inner(self) -> Inner;
    }

    /// A trait for creating std types from internal representations
    #[doc(hidden)]
    pub trait FromInner<Inner> {
        fn from_inner(inner: Inner) -> Self;
    }

    /// Enqueues a procedure to run when the main thread exits.
    ///
    /// Currently these closures are only run once the main *Rust* thread exits.
    /// Once the `at_exit` handlers begin running, more may be enqueued, but not
    /// infinitely so. Eventually a handler registration will be forced to fail.
    ///
    /// Returns `Ok` if the handler was successfully registered, meaning that the
    /// closure will be run once the main thread exits. Returns `Err` to indicate
    /// that the closure could not be registered, meaning that it is not scheduled
    /// to be run.
    pub fn at_exit<F: FnOnce() + Send + 'static>(f: F) -> Result<(), ()> {
        if at_exit_imp::push(Box::new(f)) {Ok(())} else {Err(())}
    }

    macro_rules! rtabort {
        ($($t:tt)*) => (::sys_common::util::abort(format_args!($($t)*)))
    }

    /// One-time runtime cleanup.
    pub fn cleanup() {
        static CLEANUP: Once = Once::new();
        CLEANUP.call_once(|| unsafe {
            sys::args::cleanup();
            sys::stack_overflow::cleanup();
            at_exit_imp::cleanup();
        });
    }

    // 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).
    #[allow(dead_code)] // not used on all platforms
    pub fn mul_div_u64(value: u64, numer: u64, denom: u64) -> u64 {
        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_u64( 1_000_000_000_001, 1_000_000_000, 1_000_000),
                   1_000_000_000_001_000);
    }

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