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</pre></div><pre class="rust"><code><span class="kw">use crate</span>::<span class="kw-2">*</span>;
<span class="doccomment">/// function bodies from the alloc_layout_extra feature that I want to use on stable. Very much
/// robbery on my part, so credit to whoever wrote these originally
</span><span class="kw">mod </span>alloc_layout_extra {
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="kw">pub const fn </span>padding_needed_for(layout: <span class="kw-2">&</span>Layout, align: usize) -> usize {
<span class="kw">let </span>len = layout.size();
<span class="comment">// Rounded up value is:
// len_rounded_up = (len + align - 1) & !(align - 1);
// and then we return the padding difference: `len_rounded_up - len`.
//
// We use modular arithmetic throughout:
//
// 1. align is guaranteed to be > 0, so align - 1 is always
// valid.
//
// 2. `len + align - 1` can overflow by at most `align - 1`,
// so the &-mask with `!(align - 1)` will ensure that in the
// case of overflow, `len_rounded_up` will itself be 0.
// Thus the returned padding, when added to `len`, yields 0,
// which trivially satisfies the alignment `align`.
//
// (Of course, attempts to allocate blocks of memory whose
// size and padding overflow in the above manner should cause
// the allocator to yield an error anyway.)
</span><span class="kw">let </span>len_rounded_up = len.wrapping_add(align).wrapping_sub(<span class="number">1</span>) & !align.wrapping_sub(<span class="number">1</span>);
len_rounded_up.wrapping_sub(len)
}
<span class="kw">pub fn </span>repeat(layout: <span class="kw-2">&</span>Layout, n: usize) -> <span class="prelude-ty">Option</span><(Layout, usize)> {
<span class="comment">// This cannot overflow. Quoting from the invariant of Layout:
// > `size`, when rounded up to the nearest multiple of `align`,
// > must not overflow isize (i.e., the rounded value must be
// > less than or equal to `isize::MAX`)
</span><span class="kw">let </span>padded_size = layout.size() + padding_needed_for(layout, layout.align());
<span class="kw">let </span>alloc_size = padded_size.checked_mul(n)<span class="question-mark">?</span>;
<span class="comment">// The safe constructor is called here to enforce the isize size limit.
</span><span class="kw">let </span>layout = Layout::from_size_align(alloc_size, layout.align()).ok()<span class="question-mark">?</span>;
<span class="prelude-val">Some</span>((layout, padded_size))
}
}
<span class="doccomment">/// guarantees layout is non-zero
</span><span class="kw">pub fn </span>new_slice_layout<T>(capacity: usize) -> (Layout, usize) {
<span class="kw">let </span>(layout, len) =
alloc_layout_extra::repeat(<span class="kw-2">&</span>Layout::new::<T>(), capacity).expect(<span class="string">"capacity is valid"</span>);
<span class="kw">if </span>layout.size() == <span class="number">0 </span>{
<span class="macro">panic!</span>(<span class="string">"cannot allocate ZST"</span>);
}
(layout, len)
}
<span class="doccomment">/// To deallocate this, make sure you multiply by `mem::size_of<T>()`.
</span><span class="kw">pub fn </span>alloc_slice<T>(count: usize) -> NonNull<[T]> {
<span class="kw">let </span>(layout, <span class="kw">_</span>) = new_slice_layout::<T>(count);
<span class="kw">let </span>(data, byte_count) = {
<span class="attr">#[cfg(feature = <span class="string">"nightly"</span>)]
</span>{
<span class="kw">let </span>data = Global
.allocate(layout)
.unwrap_or_else(|<span class="kw">_</span>| <span class="macro">panic!</span>(<span class="string">"allocation error"</span>));
(data.cast(), data.len())
}
<span class="attr">#[cfg(not(feature = <span class="string">"nightly"</span>))]
</span>{
<span class="kw">use </span>std::alloc::alloc;
<span class="comment">// SAFETY: new_slice_layout guarantees that layout is non-zero
</span><span class="kw">let </span>data = <span class="kw">unsafe </span>{ alloc(layout) };
<span class="kw">let </span><span class="prelude-val">Some</span>(data) = NonNull::new(data) <span class="kw">else </span>{
<span class="macro">panic!</span>(<span class="string">"allocation error"</span>)
};
(data, layout.size())
}
};
<span class="comment">// offset is the size of each allocation with padding
// let capacity = byte_count / offset;
</span><span class="kw">unsafe </span>{
<span class="comment">// SAFETY:
// - this should be valid for &'static mut [MaybeUninit], so we need to validate the safety
// contract of the creation of that type.
// - data
</span><span class="kw">let </span>raw = ptr::slice_from_raw_parts_mut(data.as_ptr() <span class="kw">as </span><span class="kw-2">*mut </span><span class="kw">_</span>, byte_count);
<span class="comment">// SAFETY: ptr is non-null, since `data.as_ptr()` is non-null
</span>NonNull::new_unchecked(raw)
}
}
<span class="doccomment">/// # Safety
/// must be a slice allocated by `unified_alloc::alloc_slice()`
</span><span class="kw">pub unsafe fn </span>dealloc_slice<T>(ptr: NonNull<[T]>) {
<span class="kw">let </span>layout = new_slice_layout::<T>(ptr.len()).<span class="number">0</span>;
<span class="attr">#[cfg(feature = <span class="string">"nightly"</span>)]
</span>{
Global.deallocate(ptr.cast(), layout);
}
<span class="attr">#[cfg(not(feature = <span class="string">"nightly"</span>))]
</span>{
<span class="kw">use </span>std::alloc::dealloc;
<span class="comment">// SAFETY: layout should be the same layout we made at the beginning, sicne it comes from
// the same function
</span><span class="kw">unsafe </span>{
dealloc(ptr.as_ptr() <span class="kw">as </span><span class="kw-2">*mut </span><span class="kw">_</span>, layout);
}
}
}
</code></pre></div></section></main></body></html>