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use std::alloc;
use std::alloc::{Layout, handle_alloc_error};
use std::{mem, cmp};

#[cfg(test)]
use std::ops::{Deref, DerefMut};
#[cfg(test)]
use std::slice;

pub(crate) struct Alloc<T> { ptr: *mut T, len: usize, align: usize }

impl<T> Alloc<T> {
    #[inline]
    pub unsafe fn new(nelem: usize, align: usize) -> Self {
        let align = cmp::max(align, mem::align_of::<T>());
        #[cfg(debug_assertions)]
        let layout = Layout::from_size_align(mem::size_of::<T>() * nelem, align).unwrap();
        #[cfg(not(debug_assertions))]
        let layout = Layout::from_size_align_unchecked(mem::size_of::<T>() * nelem, align);
        dprint!("Allocating nelem={}, layout={:?}", nelem, layout);
        let ptr = alloc::alloc(layout);
        if ptr.is_null() {
            handle_alloc_error(layout);
        }
        Alloc {
            ptr: ptr as *mut T,
            len: nelem,
            align,
        }
    }

    #[cfg(test)]
    pub fn init_with(mut self, elt: T) -> Alloc<T> where T: Copy
    {
        for elt1 in &mut self[..] {
            *elt1 = elt;
        }
        self
    }

    #[inline]
    pub fn ptr_mut(&mut self) -> *mut T { self.ptr }
}

impl<T> Drop for Alloc<T> {
    fn drop(&mut self) {
        unsafe {
            let layout = Layout::from_size_align_unchecked(mem::size_of::<T>() * self.len, self.align);
            alloc::dealloc(self.ptr as _, layout);
        }
    }
}

#[cfg(test)]
impl<T> Deref for Alloc<T> {
    type Target = [T];
    fn deref(&self) -> &[T] {
        unsafe {
            slice::from_raw_parts(self.ptr, self.len)
        }
    }
}

#[cfg(test)]
impl<T> DerefMut for Alloc<T> {
    fn deref_mut(&mut self) -> &mut [T] {
        unsafe {
            slice::from_raw_parts_mut(self.ptr, self.len)
        }
    }
}