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    // Copyright 2014-2015 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.

    #![unstable(feature = "allocator_api",
                reason = "the precise API and guarantees it provides may be tweaked \
                          slightly, especially to possibly take into account the \
                          types being stored to make room for a future \
                          tracing garbage collector",
                issue = "32838")]

    use core::intrinsics::{min_align_of_val, size_of_val};
    use core::mem::{self, ManuallyDrop};
    use core::usize;

    pub use allocator::*;
    #[doc(hidden)]
    pub mod __core {
        pub use core::*;
    }

    extern "Rust" {
        #[allocator]
        #[rustc_allocator_nounwind]
        fn __rust_alloc(size: usize, align: usize, err: *mut u8) -> *mut u8;
        #[cold]
        #[rustc_allocator_nounwind]
        fn __rust_oom(err: *const u8) -> !;
        #[rustc_allocator_nounwind]
        fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
        #[rustc_allocator_nounwind]
        fn __rust_usable_size(layout: *const u8,
                              min: *mut usize,
                              max: *mut usize);
        #[rustc_allocator_nounwind]
        fn __rust_realloc(ptr: *mut u8,
                          old_size: usize,
                          old_align: usize,
                          new_size: usize,
                          new_align: usize,
                          err: *mut u8) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_alloc_zeroed(size: usize, align: usize, err: *mut u8) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_alloc_excess(size: usize,
                               align: usize,
                               excess: *mut usize,
                               err: *mut u8) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_realloc_excess(ptr: *mut u8,
                                 old_size: usize,
                                 old_align: usize,
                                 new_size: usize,
                                 new_align: usize,
                                 excess: *mut usize,
                                 err: *mut u8) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_grow_in_place(ptr: *mut u8,
                                old_size: usize,
                                old_align: usize,
                                new_size: usize,
                                new_align: usize) -> u8;
        #[rustc_allocator_nounwind]
        fn __rust_shrink_in_place(ptr: *mut u8,
                                  old_size: usize,
                                  old_align: usize,
                                  new_size: usize,
                                  new_align: usize) -> u8;
    }

    #[derive(Copy, Clone, Default, Debug)]
    pub struct Heap;

    unsafe impl Alloc for Heap {
        #[inline]
        unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
            let mut err = ManuallyDrop::new(mem::uninitialized::<AllocErr>());
            let ptr = __rust_alloc(layout.size(),
                                   layout.align(),
                                   &mut *err as *mut AllocErr as *mut u8);
            if ptr.is_null() {
                Err(ManuallyDrop::into_inner(err))
            } else {
                Ok(ptr)
            }
        }

        #[inline]
        #[cold]
        fn oom(&mut self, err: AllocErr) -> ! {
            unsafe {
                __rust_oom(&err as *const AllocErr as *const u8)
            }
        }

        #[inline]
        unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout) {
            __rust_dealloc(ptr, layout.size(), layout.align())
        }

        #[inline]
        fn usable_size(&self, layout: &Layout) -> (usize, usize) {
            let mut min = 0;
            let mut max = 0;
            unsafe {
                __rust_usable_size(layout as *const Layout as *const u8,
                                   &mut min,
                                   &mut max);
            }
            (min, max)
        }

        #[inline]
        unsafe fn realloc(&mut self,
                          ptr: *mut u8,
                          layout: Layout,
                          new_layout: Layout)
                          -> Result<*mut u8, AllocErr>
        {
            let mut err = ManuallyDrop::new(mem::uninitialized::<AllocErr>());
            let ptr = __rust_realloc(ptr,
                                     layout.size(),
                                     layout.align(),
                                     new_layout.size(),
                                     new_layout.align(),
                                     &mut *err as *mut AllocErr as *mut u8);
            if ptr.is_null() {
                Err(ManuallyDrop::into_inner(err))
            } else {
                mem::forget(err);
                Ok(ptr)
            }
        }

        #[inline]
        unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
            let mut err = ManuallyDrop::new(mem::uninitialized::<AllocErr>());
            let ptr = __rust_alloc_zeroed(layout.size(),
                                          layout.align(),
                                          &mut *err as *mut AllocErr as *mut u8);
            if ptr.is_null() {
                Err(ManuallyDrop::into_inner(err))
            } else {
                Ok(ptr)
            }
        }

        #[inline]
        unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
            let mut err = ManuallyDrop::new(mem::uninitialized::<AllocErr>());
            let mut size = 0;
            let ptr = __rust_alloc_excess(layout.size(),
                                          layout.align(),
                                          &mut size,
                                          &mut *err as *mut AllocErr as *mut u8);
            if ptr.is_null() {
                Err(ManuallyDrop::into_inner(err))
            } else {
                Ok(Excess(ptr, size))
            }
        }

        #[inline]
        unsafe fn realloc_excess(&mut self,
                                 ptr: *mut u8,
                                 layout: Layout,
                                 new_layout: Layout) -> Result<Excess, AllocErr> {
            let mut err = ManuallyDrop::new(mem::uninitialized::<AllocErr>());
            let mut size = 0;
            let ptr = __rust_realloc_excess(ptr,
                                            layout.size(),
                                            layout.align(),
                                            new_layout.size(),
                                            new_layout.align(),
                                            &mut size,
                                            &mut *err as *mut AllocErr as *mut u8);
            if ptr.is_null() {
                Err(ManuallyDrop::into_inner(err))
            } else {
                Ok(Excess(ptr, size))
            }
        }

        #[inline]
        unsafe fn grow_in_place(&mut self,
                                ptr: *mut u8,
                                layout: Layout,
                                new_layout: Layout)
                                -> Result<(), CannotReallocInPlace>
        {
            debug_assert!(new_layout.size() >= layout.size());
            debug_assert!(new_layout.align() == layout.align());
            let ret = __rust_grow_in_place(ptr,
                                           layout.size(),
                                           layout.align(),
                                           new_layout.size(),
                                           new_layout.align());
            if ret != 0 {
                Ok(())
            } else {
                Err(CannotReallocInPlace)
            }
        }

        #[inline]
        unsafe fn shrink_in_place(&mut self,
                                  ptr: *mut u8,
                                  layout: Layout,
                                  new_layout: Layout) -> Result<(), CannotReallocInPlace> {
            debug_assert!(new_layout.size() <= layout.size());
            debug_assert!(new_layout.align() == layout.align());
            let ret = __rust_shrink_in_place(ptr,
                                             layout.size(),
                                             layout.align(),
                                             new_layout.size(),
                                             new_layout.align());
            if ret != 0 {
                Ok(())
            } else {
                Err(CannotReallocInPlace)
            }
        }
    }

    /// An arbitrary non-null address to represent zero-size allocations.
    ///
    /// This preserves the non-null invariant for types like `Box<T>`. The address
    /// may overlap with non-zero-size memory allocations.
    #[rustc_deprecated(since = "1.19", reason = "Use Unique/Shared::empty() instead")]
    #[unstable(feature = "heap_api", issue = "27700")]
    pub const EMPTY: *mut () = 1 as *mut ();

    /// The allocator for unique pointers.
    // This function must not unwind. If it does, MIR trans will fail.
    #[cfg(not(test))]
    #[lang = "exchange_malloc"]
    #[inline]
    unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
        if size == 0 {
            align as *mut u8
        } else {
            let layout = Layout::from_size_align_unchecked(size, align);
            Heap.alloc(layout).unwrap_or_else(|err| {
                Heap.oom(err)
            })
        }
    }

    #[cfg_attr(not(test), lang = "box_free")]
    #[inline]
    pub(crate) unsafe fn box_free<T: ?Sized>(ptr: *mut T) {
        let size = size_of_val(&*ptr);
        let align = min_align_of_val(&*ptr);
        // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
        if size != 0 {
            let layout = Layout::from_size_align_unchecked(size, align);
            Heap.dealloc(ptr as *mut u8, layout);
        }
    }

    #[cfg(test)]
    mod tests {
        extern crate test;
        use self::test::Bencher;
        use boxed::Box;
        use heap::{Heap, Alloc, Layout};

        #[test]
        fn allocate_zeroed() {
            unsafe {
                let layout = Layout::from_size_align(1024, 1).unwrap();
                let ptr = Heap.alloc_zeroed(layout.clone())
                    .unwrap_or_else(|e| Heap.oom(e));

                let end = ptr.offset(layout.size() as isize);
                let mut i = ptr;
                while i < end {
                    assert_eq!(*i, 0);
                    i = i.offset(1);
                }
                Heap.dealloc(ptr, layout);
            }
        }

        #[bench]
        fn alloc_owned_small(b: &mut Bencher) {
            b.iter(|| {
                let _: Box<_> = box 10;
            })
        }
    }

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