// Seemingly inconsequential code changes to this file can lead to measurable

// performance impact on compilation times, due at least in part to the fact

// that the layout code gets called from many instantiations of the various

// collections, resulting in having to optimize down excess IR multiple times.

// Your performance intuition is useless. Run perf.

#[cfg(not(feature = "ferrocene_certified"))]

use crate::error::Error;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::intrinsics::{unchecked_add, unchecked_mul, unchecked_sub};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::mem::SizedTypeProperties;

#[cfg(not(feature = "ferrocene_certified"))]

use crate::ptr::{Alignment, NonNull};

#[cfg(not(feature = "ferrocene_certified"))]

use crate::{assert_unsafe_precondition, fmt, mem};

#[cfg(feature = "ferrocene_certified")]

use crate::{assert_unsafe_precondition, intrinsics::unchecked_sub, mem, ptr::Alignment};

// While this function is used in one place and its implementation

// could be inlined, the previous attempts to do so made rustc

// slower:

//

// * https://github.com/rust-lang/rust/pull/72189

// * https://github.com/rust-lang/rust/pull/79827

/// Layout of a block of memory.

///

/// An instance of `Layout` describes a particular layout of memory.

/// You build a `Layout` up as an input to give to an allocator.

///

/// All layouts have an associated size and a power-of-two alignment. The size, when rounded up to

/// the nearest multiple of `align`, does not overflow `isize` (i.e., the rounded value will always be

/// less than or equal to `isize::MAX`).

///

/// (Note that layouts are *not* required to have non-zero size,

/// even though `GlobalAlloc` requires that all memory requests

/// be non-zero in size. A caller must either ensure that conditions

/// like this are met, use specific allocators with looser

/// requirements, or use the more lenient `Allocator` interface.)

#[stable(feature = "alloc_layout", since = "1.28.0")]

#[cfg_attr(not(feature = "ferrocene_certified"), derive(Copy, Clone, Debug, PartialEq, Eq, Hash))]

#[lang = "alloc_layout"]

pub struct Layout {

    // size of the requested block of memory, measured in bytes.

    size: usize,

    // alignment of the requested block of memory, measured in bytes.

    // we ensure that this is always a power-of-two, because API's

    // like `posix_memalign` require it and it is a reasonable

    // constraint to impose on Layout constructors.

    //

    // (However, we do not analogously require `align >= sizeof(void*)`,

    //  even though that is *also* a requirement of `posix_memalign`.)

    align: Alignment,

}

impl Layout {

    /// Constructs a `Layout` from a given `size` and `align`,

    /// or returns `LayoutError` if any of the following conditions

    /// are not met:

    ///

    /// * `align` must not be zero,

    ///

    /// * `align` must be a power of two,

    ///

    /// * `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`).

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "const_alloc_layout_size_align", since = "1.50.0")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn from_size_align(size: usize, align: usize) -> Result<Self, LayoutError> {

        if Layout::is_size_align_valid(size, align) {

            // SAFETY: Layout::is_size_align_valid checks the preconditions for this call.

            unsafe { Ok(Layout { size, align: mem::transmute(align) }) }

        } else {

            Err(LayoutError)

        }

    }

    const fn is_size_align_valid(size: usize, align: usize) -> bool {

        let Some(align) = Alignment::new(align) else { return false };

        if size > Self::max_size_for_align(align) {

            return false;

        }

        true

    }

    #[inline(always)]

        // (power-of-two implies align != 0.)

        // Rounded up size is:

        //   size_rounded_up = (size + align - 1) & !(align - 1);

        //

        // We know from above that align != 0. If adding (align - 1)

        // does not overflow, then rounding up will be fine.

        //

        // Conversely, &-masking with !(align - 1) will subtract off

        // only low-order-bits. Thus if overflow occurs with the sum,

        // the &-mask cannot subtract enough to undo that overflow.

        //

        // Above implies that checking for summation overflow is both

        // necessary and sufficient.

        // SAFETY: the maximum possible alignment is `isize::MAX + 1`,

        // so the subtraction cannot overflow.

    /// Internal helper constructor to skip revalidating alignment validity.

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    const fn from_size_alignment(size: usize, align: Alignment) -> Result<Self, LayoutError> {

        if size > Self::max_size_for_align(align) {

            return Err(LayoutError);

        }

        // SAFETY: Layout::size invariants checked above.

        Ok(Layout { size, align })

    }

    /// Creates a layout, bypassing all checks.

    ///

    /// # Safety

    ///

    /// This function is unsafe as it does not verify the preconditions from

    /// [`Layout::from_size_align`].

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "const_alloc_layout_unchecked", since = "1.36.0")]

    #[must_use]

    #[inline]

    #[track_caller]

            check_library_ub,

            "Layout::from_size_align_unchecked requires that align is a power of 2 \

            and the rounded-up allocation size does not exceed isize::MAX",

            (

            ) => Layout::is_size_align_valid(size, align)

        );

        // SAFETY: the caller is required to uphold the preconditions.

    /// The minimum size in bytes for a memory block of this layout.

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "const_alloc_layout_size_align", since = "1.50.0")]

    #[must_use]

    #[inline]

    /// The minimum byte alignment for a memory block of this layout.

    ///

    /// The returned alignment is guaranteed to be a power of two.

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "const_alloc_layout_size_align", since = "1.50.0")]

    #[must_use = "this returns the minimum alignment, \

                  without modifying the layout"]

    #[inline]

    /// Constructs a `Layout` suitable for holding a value of type `T`.

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "alloc_layout_const_new", since = "1.42.0")]

    #[must_use]

    #[inline]

        // SAFETY: if the type is instantiated, rustc already ensures that its

        // layout is valid. Use the unchecked constructor to avoid inserting a

        // panicking codepath that needs to be optimized out.

    /// Produces layout describing a record that could be used to

    /// allocate backing structure for `T` (which could be a trait

    /// or other unsized type like a slice).

    #[stable(feature = "alloc_layout", since = "1.28.0")]

    #[rustc_const_stable(feature = "const_alloc_layout", since = "1.85.0")]

    #[must_use]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn for_value<T: ?Sized>(t: &T) -> Self {

        let (size, align) = (size_of_val(t), align_of_val(t));

        // SAFETY: see rationale in `new` for why this is using the unsafe variant

        unsafe { Layout::from_size_align_unchecked(size, align) }

    }

    /// Produces layout describing a record that could be used to

    /// allocate backing structure for `T` (which could be a trait

    /// or other unsized type like a slice).

    ///

    /// # Safety

    ///

    /// This function is only safe to call if the following conditions hold:

    ///

    /// - If `T` is `Sized`, this function is always safe to call.

    /// - If the unsized tail of `T` is:

    ///     - a [slice], then the length of the slice tail must be an initialized

    ///       integer, and the size of the *entire value*

    ///       (dynamic tail length + statically sized prefix) must fit in `isize`.

    ///       For the special case where the dynamic tail length is 0, this function

    ///       is safe to call.

    ///     - a [trait object], then the vtable part of the pointer must point

    ///       to a valid vtable for the type `T` acquired by an unsizing coercion,

    ///       and the size of the *entire value*

    ///       (dynamic tail length + statically sized prefix) must fit in `isize`.

    ///     - an (unstable) [extern type], then this function is always safe to

    ///       call, but may panic or otherwise return the wrong value, as the

    ///       extern type's layout is not known. This is the same behavior as

    ///       [`Layout::for_value`] on a reference to an extern type tail.

    ///     - otherwise, it is conservatively not allowed to call this function.

    ///

    /// [trait object]: ../../book/ch17-02-trait-objects.html

    /// [extern type]: ../../unstable-book/language-features/extern-types.html

    #[unstable(feature = "layout_for_ptr", issue = "69835")]

    #[must_use]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const unsafe fn for_value_raw<T: ?Sized>(t: *const T) -> Self {

        // SAFETY: we pass along the prerequisites of these functions to the caller

        let (size, align) = unsafe { (mem::size_of_val_raw(t), mem::align_of_val_raw(t)) };

        // SAFETY: see rationale in `new` for why this is using the unsafe variant

        unsafe { Layout::from_size_align_unchecked(size, align) }

    }

    /// Creates a `NonNull` that is dangling, but well-aligned for this Layout.

    ///

    /// Note that the address of the returned pointer may potentially

    /// be that of a valid pointer, which means this must not be used

    /// as a "not yet initialized" sentinel value.

    /// Types that lazily allocate must track initialization by some other means.

    #[unstable(feature = "alloc_layout_extra", issue = "55724")]

    #[must_use]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn dangling(&self) -> NonNull<u8> {

        NonNull::without_provenance(self.align.as_nonzero())

    }

    /// Creates a layout describing the record that can hold a value

    /// of the same layout as `self`, but that also is aligned to

    /// alignment `align` (measured in bytes).

    ///

    /// If `self` already meets the prescribed alignment, then returns

    /// `self`.

    ///

    /// Note that this method does not add any padding to the overall

    /// size, regardless of whether the returned layout has a different

    /// alignment. In other words, if `K` has size 16, `K.align_to(32)`

    /// will *still* have size 16.

    ///

    /// Returns an error if the combination of `self.size()` and the given

    /// `align` violates the conditions listed in [`Layout::from_size_align`].

    #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]

    #[rustc_const_stable(feature = "const_alloc_layout", since = "1.85.0")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn align_to(&self, align: usize) -> Result<Self, LayoutError> {

        if let Some(align) = Alignment::new(align) {

            Layout::from_size_alignment(self.size, Alignment::max(self.align, align))

        } else {

            Err(LayoutError)

        }

    }

    /// Returns the amount of padding we must insert after `self`

    /// to ensure that the following address will satisfy `align`

    /// (measured in bytes).

    ///

    /// e.g., if `self.size()` is 9, then `self.padding_needed_for(4)`

    /// returns 3, because that is the minimum number of bytes of

    /// padding required to get a 4-aligned address (assuming that the

    /// corresponding memory block starts at a 4-aligned address).

    ///

    /// The return value of this function has no meaning if `align` is

    /// not a power-of-two.

    ///

    /// Note that the utility of the returned value requires `align`

    /// to be less than or equal to the alignment of the starting

    /// address for the whole allocated block of memory. One way to

    /// satisfy this constraint is to ensure `align <= self.align()`.

    #[unstable(feature = "alloc_layout_extra", issue = "55724")]

    #[must_use = "this returns the padding needed, \

                  without modifying the `Layout`"]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn padding_needed_for(&self, align: usize) -> usize {

        // FIXME: Can we just change the type on this to `Alignment`?

        let Some(align) = Alignment::new(align) else { return usize::MAX };

        let len_rounded_up = self.size_rounded_up_to_custom_align(align);

        // SAFETY: Cannot overflow because the rounded-up value is never less

        unsafe { unchecked_sub(len_rounded_up, self.size) }

    }

    /// Returns the smallest multiple of `align` greater than or equal to `self.size()`.

    ///

    /// This can return at most `Alignment::MAX` (aka `isize::MAX + 1`)

    /// because the original size is at most `isize::MAX`.

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    const fn size_rounded_up_to_custom_align(&self, align: Alignment) -> usize {

        // SAFETY:

        // Rounded up value is:

        //   size_rounded_up = (size + align - 1) & !(align - 1);

        //

        // The arithmetic we do here can never overflow:

        //

        // 1. align is guaranteed to be > 0, so align - 1 is always

        //    valid.

        //

        // 2. size is at most `isize::MAX`, so adding `align - 1` (which is at

        //    most `isize::MAX`) can never overflow a `usize`.

        //

        // 3. masking by the alignment can remove at most `align - 1`,

        //    which is what we just added, thus the value we return is never

        //    less than the original `size`.

        //

        // (Size 0 Align MAX is already aligned, so stays the same, but things like

        // Size 1 Align MAX or Size isize::MAX Align 2 round up to `isize::MAX + 1`.)

        unsafe {

            let align_m1 = unchecked_sub(align.as_usize(), 1);

            let size_rounded_up = unchecked_add(self.size, align_m1) & !align_m1;

            size_rounded_up

        }

    }

    /// Creates a layout by rounding the size of this layout up to a multiple

    /// of the layout's alignment.

    ///

    /// This is equivalent to adding the result of `padding_needed_for`

    /// to the layout's current size.

    #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]

    #[rustc_const_stable(feature = "const_alloc_layout", since = "1.85.0")]

    #[must_use = "this returns a new `Layout`, \

                  without modifying the original"]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn pad_to_align(&self) -> Layout {

        // 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`)

        let new_size = self.size_rounded_up_to_custom_align(self.align);

        // SAFETY: padded size is guaranteed to not exceed `isize::MAX`.

        unsafe { Layout::from_size_align_unchecked(new_size, self.align()) }

    }

    /// Creates a layout describing the record for `n` instances of

    /// `self`, with a suitable amount of padding between each to

    /// ensure that each instance is given its requested size and

    /// alignment. On success, returns `(k, offs)` where `k` is the

    /// layout of the array and `offs` is the distance between the start

    /// of each element in the array.

    ///

    /// (That distance between elements is sometimes known as "stride".)

    ///

    /// On arithmetic overflow, returns `LayoutError`.

    ///

    /// # Examples

    ///

    /// ```

    /// #![feature(alloc_layout_extra)]

    /// use std::alloc::Layout;

    ///

    /// // All rust types have a size that's a multiple of their alignment.

    /// let normal = Layout::from_size_align(12, 4).unwrap();

    /// let repeated = normal.repeat(3).unwrap();

    /// assert_eq!(repeated, (Layout::from_size_align(36, 4).unwrap(), 12));

    ///

    /// // But you can manually make layouts which don't meet that rule.

    /// let padding_needed = Layout::from_size_align(6, 4).unwrap();

    /// let repeated = padding_needed.repeat(3).unwrap();

    /// assert_eq!(repeated, (Layout::from_size_align(24, 4).unwrap(), 8));

    /// ```

    #[unstable(feature = "alloc_layout_extra", issue = "55724")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn repeat(&self, n: usize) -> Result<(Self, usize), LayoutError> {

        let padded = self.pad_to_align();

        if let Ok(repeated) = padded.repeat_packed(n) {

            Ok((repeated, padded.size()))

        } else {

            Err(LayoutError)

        }

    }

    /// Creates a layout describing the record for `self` followed by

    /// `next`, including any necessary padding to ensure that `next`

    /// will be properly aligned, but *no trailing padding*.

    ///

    /// In order to match C representation layout `repr(C)`, you should

    /// call `pad_to_align` after extending the layout with all fields.

    /// (There is no way to match the default Rust representation

    /// layout `repr(Rust)`, as it is unspecified.)

    ///

    /// Note that the alignment of the resulting layout will be the maximum of

    /// those of `self` and `next`, in order to ensure alignment of both parts.

    ///

    /// Returns `Ok((k, offset))`, where `k` is layout of the concatenated

    /// record and `offset` is the relative location, in bytes, of the

    /// start of the `next` embedded within the concatenated record

    /// (assuming that the record itself starts at offset 0).

    ///

    /// On arithmetic overflow, returns `LayoutError`.

    ///

    /// # Examples

    ///

    /// To calculate the layout of a `#[repr(C)]` structure and the offsets of

    /// the fields from its fields' layouts:

    ///

    /// ```rust

    /// # use std::alloc::{Layout, LayoutError};

    /// pub fn repr_c(fields: &[Layout]) -> Result<(Layout, Vec<usize>), LayoutError> {

    ///     let mut offsets = Vec::new();

    ///     let mut layout = Layout::from_size_align(0, 1)?;

    ///     for &field in fields {

    ///         let (new_layout, offset) = layout.extend(field)?;

    ///         layout = new_layout;

    ///         offsets.push(offset);

    ///     }

    ///     // Remember to finalize with `pad_to_align`!

    ///     Ok((layout.pad_to_align(), offsets))

    /// }

    /// # // test that it works

    /// # #[repr(C)] struct S { a: u64, b: u32, c: u16, d: u32 }

    /// # let s = Layout::new::<S>();

    /// # let u16 = Layout::new::<u16>();

    /// # let u32 = Layout::new::<u32>();

    /// # let u64 = Layout::new::<u64>();

    /// # assert_eq!(repr_c(&[u64, u32, u16, u32]), Ok((s, vec![0, 8, 12, 16])));

    /// ```

    #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]

    #[rustc_const_stable(feature = "const_alloc_layout", since = "1.85.0")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn extend(&self, next: Self) -> Result<(Self, usize), LayoutError> {

        let new_align = Alignment::max(self.align, next.align);

        let offset = self.size_rounded_up_to_custom_align(next.align);

        // SAFETY: `offset` is at most `isize::MAX + 1` (such as from aligning

        // to `Alignment::MAX`) and `next.size` is at most `isize::MAX` (from the

        // `Layout` type invariant).  Thus the largest possible `new_size` is

        // `isize::MAX + 1 + isize::MAX`, which is `usize::MAX`, and cannot overflow.

        let new_size = unsafe { unchecked_add(offset, next.size) };

        if let Ok(layout) = Layout::from_size_alignment(new_size, new_align) {

            Ok((layout, offset))

        } else {

            Err(LayoutError)

        }

    }

    /// Creates a layout describing the record for `n` instances of

    /// `self`, with no padding between each instance.

    ///

    /// Note that, unlike `repeat`, `repeat_packed` does not guarantee

    /// that the repeated instances of `self` will be properly

    /// aligned, even if a given instance of `self` is properly

    /// aligned. In other words, if the layout returned by

    /// `repeat_packed` is used to allocate an array, it is not

    /// guaranteed that all elements in the array will be properly

    /// aligned.

    ///

    /// On arithmetic overflow, returns `LayoutError`.

    #[unstable(feature = "alloc_layout_extra", issue = "55724")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn repeat_packed(&self, n: usize) -> Result<Self, LayoutError> {

        if let Some(size) = self.size.checked_mul(n) {

            // The safe constructor is called here to enforce the isize size limit.

            Layout::from_size_alignment(size, self.align)

        } else {

            Err(LayoutError)

        }

    }

    /// Creates a layout describing the record for `self` followed by

    /// `next` with no additional padding between the two. Since no

    /// padding is inserted, the alignment of `next` is irrelevant,

    /// and is not incorporated *at all* into the resulting layout.

    ///

    /// On arithmetic overflow, returns `LayoutError`.

    #[unstable(feature = "alloc_layout_extra", issue = "55724")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn extend_packed(&self, next: Self) -> Result<Self, LayoutError> {

        // SAFETY: each `size` is at most `isize::MAX == usize::MAX/2`, so the

        // sum is at most `usize::MAX/2*2 == usize::MAX - 1`, and cannot overflow.

        let new_size = unsafe { unchecked_add(self.size, next.size) };

        // The safe constructor enforces that the new size isn't too big for the alignment

        Layout::from_size_alignment(new_size, self.align)

    }

    /// Creates a layout describing the record for a `[T; n]`.

    ///

    /// On arithmetic overflow or when the total size would exceed

    /// `isize::MAX`, returns `LayoutError`.

    #[stable(feature = "alloc_layout_manipulation", since = "1.44.0")]

    #[rustc_const_stable(feature = "const_alloc_layout", since = "1.85.0")]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn array<T>(n: usize) -> Result<Self, LayoutError> {

        // Reduce the amount of code we need to monomorphize per `T`.

        return inner(T::LAYOUT, n);

        #[inline]

        const fn inner(element_layout: Layout, n: usize) -> Result<Layout, LayoutError> {

            let Layout { size: element_size, align } = element_layout;

            // We need to check two things about the size:

            //  - That the total size won't overflow a `usize`, and

            //  - That the total size still fits in an `isize`.

            // By using division we can check them both with a single threshold.

            // That'd usually be a bad idea, but thankfully here the element size

            // and alignment are constants, so the compiler will fold all of it.

            if element_size != 0 && n > Layout::max_size_for_align(align) / element_size {

                return Err(LayoutError);

            }

            // SAFETY: We just checked that we won't overflow `usize` when we multiply.

            // This is a useless hint inside this function, but after inlining this helps

            // deduplicate checks for whether the overall capacity is zero (e.g., in RawVec's

            // allocation path) before/after this multiplication.

            let array_size = unsafe { unchecked_mul(element_size, n) };

            // SAFETY: We just checked above that the `array_size` will not

            // exceed `isize::MAX` even when rounded up to the alignment.

            // And `Alignment` guarantees it's a power of two.

            unsafe { Ok(Layout::from_size_align_unchecked(array_size, align.as_usize())) }

        }

    }

    /// Perma-unstable access to `align` as `Alignment` type.

    #[unstable(issue = "none", feature = "std_internals")]

    #[doc(hidden)]

    #[inline]

    #[cfg(not(feature = "ferrocene_certified"))]

    pub const fn alignment(&self) -> Alignment {

        self.align

    }

}

#[stable(feature = "alloc_layout", since = "1.28.0")]

#[deprecated(

    since = "1.52.0",

    note = "Name does not follow std convention, use LayoutError",

    suggestion = "LayoutError"

)]

#[cfg(not(feature = "ferrocene_certified"))]

pub type LayoutErr = LayoutError;

/// The `LayoutError` is returned when the parameters given

/// to `Layout::from_size_align`

/// or some other `Layout` constructor

/// do not satisfy its documented constraints.

#[stable(feature = "alloc_layout_error", since = "1.50.0")]

#[non_exhaustive]

#[derive(Clone, PartialEq, Eq, Debug)]

#[cfg(not(feature = "ferrocene_certified"))]

pub struct LayoutError;

#[stable(feature = "alloc_layout", since = "1.28.0")]

#[cfg(not(feature = "ferrocene_certified"))]

impl Error for LayoutError {}

// (we need this for downstream impl of trait Error)

#[stable(feature = "alloc_layout", since = "1.28.0")]

#[cfg(not(feature = "ferrocene_certified"))]

impl fmt::Display for LayoutError {

    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

        f.write_str("invalid parameters to Layout::from_size_align")

    }

}