// This file is part of libfringe, a low-level green threading library.
// Copyright (c) whitequark <whitequark@whitequark.org>
// See the LICENSE file included in this distribution.
extern crate alloc;

use core::slice;
use self::alloc::heap;
use self::alloc::boxed::Box;
use stack::Stack;

/// OwnedStack holds a non-guarded, heap-allocated stack.
#[derive(Debug)]
pub struct OwnedStack(Box<[u8]>);

impl OwnedStack {
    /// Allocates a new stack with exactly `size` accessible bytes and alignment appropriate
    /// for the current platform using the default Rust allocator.
    pub fn new(size: usize) -> OwnedStack {
        unsafe {
            let aligned_size = size & !(::STACK_ALIGNMENT - 1);
            let ptr = heap::allocate(aligned_size, ::STACK_ALIGNMENT);
            OwnedStack(Box::from_raw(slice::from_raw_parts_mut(ptr, aligned_size)))
        }
    }
}

unsafe impl Stack for OwnedStack {
    #[inline(always)]
    fn base(&self) -> *mut u8 {
        // The slice cannot wrap around the address space, so the conversion from usize
        // to isize will not wrap either.
        let len = self.0.len() as isize;
        unsafe { self.limit().offset(len) }
    }

    #[inline(always)]
    fn limit(&self) -> *mut u8 {
        self.0.as_ptr() as *mut u8
    }
}