#![allow(dead_code)]

use crate::Error;

use core::{mem::MaybeUninit, ptr, slice};

/// Polyfill for `maybe_uninit_slice` feature's

/// `MaybeUninit::slice_assume_init_mut`. Every element of `slice` must have

/// been initialized.

#[inline(always)]

pub unsafe fn slice_assume_init_mut<T>(slice: &mut [MaybeUninit<T>]) -> &mut [T] {

    let ptr = ptr::from_mut(slice) as *mut [T];

    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.

    unsafe { &mut *ptr }

}

Unexecuted instantiation: getrandom::util::slice_assume_init_mut::<u8>

Unexecuted instantiation: getrandom::util::slice_assume_init_mut::<_>

#[inline]

pub fn uninit_slice_fill_zero(slice: &mut [MaybeUninit<u8>]) -> &mut [u8] {

    unsafe { ptr::write_bytes(slice.as_mut_ptr(), 0, slice.len()) };

    unsafe { slice_assume_init_mut(slice) }

}

#[inline(always)]

pub fn slice_as_uninit<T>(slice: &[T]) -> &[MaybeUninit<T>] {

    let ptr = ptr::from_ref(slice) as *const [MaybeUninit<T>];

    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.

    unsafe { &*ptr }

}

/// View an mutable initialized array as potentially-uninitialized.

///

/// This is unsafe because it allows assigning uninitialized values into

/// `slice`, which would be undefined behavior.

#[inline(always)]

pub unsafe fn slice_as_uninit_mut<T>(slice: &mut [T]) -> &mut [MaybeUninit<T>] {

    let ptr = ptr::from_mut(slice) as *mut [MaybeUninit<T>];

    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.

    unsafe { &mut *ptr }

}

/// Default implementation of `inner_u32` on top of `fill_uninit`

#[inline]

pub fn inner_u32() -> Result<u32, Error> {

    let mut res = MaybeUninit::<u32>::uninit();

    // SAFETY: the created slice has the same size as `res`

    let dst = unsafe {

        let p: *mut MaybeUninit<u8> = res.as_mut_ptr().cast();

        slice::from_raw_parts_mut(p, core::mem::size_of::<u32>())

    };

    crate::fill_uninit(dst)?;

    // SAFETY: `dst` has been fully initialized by `imp::fill_inner`

    // since it returned `Ok`.

    Ok(unsafe { res.assume_init() })

}

/// Default implementation of `inner_u64` on top of `fill_uninit`

#[inline]

pub fn inner_u64() -> Result<u64, Error> {

    let mut res = MaybeUninit::<u64>::uninit();

    // SAFETY: the created slice has the same size as `res`

    let dst = unsafe {

        let p: *mut MaybeUninit<u8> = res.as_mut_ptr().cast();

        slice::from_raw_parts_mut(p, core::mem::size_of::<u64>())

    };

    crate::fill_uninit(dst)?;

    // SAFETY: `dst` has been fully initialized by `imp::fill_inner`

    // since it returned `Ok`.

    Ok(unsafe { res.assume_init() })

}

Unexecuted instantiation: getrandom::util::inner_u64

Unexecuted instantiation: getrandom::util::inner_u64

/// Truncates `u64` and returns the lower 32 bits as `u32`

pub(crate) fn truncate(val: u64) -> u32 {

    u32::try_from(val & u64::from(u32::MAX)).expect("The higher 32 bits are masked")

}