1//! Miscellaneous minor utilities.
2
3#![allow(dead_code)]
4#![allow(unused_macros)]
5
6use core::ffi::c_void;
7use core::mem::{align_of, size_of};
8use core::ptr::{null, null_mut, NonNull};
9
10/// Convert a `&T` into a `*const T` without using an `as`.
11#[inline]
12pub(crate) const fn as_ptr<T>(t: &T) -> *const T {
13 t
14}
15
16/// Convert a `&mut T` into a `*mut T` without using an `as`.
17#[inline]
18pub(crate) fn as_mut_ptr<T>(t: &mut T) -> *mut T {
19 t
20}
21
22/// Convert an `Option<&T>` into a possibly-null `*const T`.
23#[inline]
24pub(crate) const fn option_as_ptr<T>(t: Option<&T>) -> *const T {
25 match t {
26 Some(t: &T) => t,
27 None => null(),
28 }
29}
30
31/// Convert an `Option<&mut T>` into a possibly-null `*mut T`.
32#[inline]
33pub(crate) fn option_as_mut_ptr<T>(t: Option<&mut T>) -> *mut T {
34 match t {
35 Some(t: &mut T) => t,
36 None => null_mut(),
37 }
38}
39
40/// Convert a `*mut c_void` to a `*mut T`, checking that it is not null,
41/// misaligned, or pointing to a region of memory that wraps around the address
42/// space.
43pub(crate) fn check_raw_pointer<T>(value: *mut c_void) -> Option<NonNull<T>> {
44 if (value as usize).checked_add(size_of::<T>()).is_none()
45 || (value as usize) % align_of::<T>() != 0
46 {
47 return None;
48 }
49
50 NonNull::new(ptr:value.cast())
51}
52
53/// Create a union value containing a default value in one of its arms.
54///
55/// The field names a union field which must have the same size as the union
56/// itself.
57macro_rules! default_union {
58 ($union:ident, $field:ident) => {{
59 let u = $union {
60 $field: Default::default(),
61 };
62
63 // Assert that the given field initializes the whole union.
64 #[cfg(test)]
65 unsafe {
66 let field_value = u.$field;
67 assert_eq!(
68 core::mem::size_of_val(&u),
69 core::mem::size_of_val(&field_value)
70 );
71 const_assert_eq!(memoffset::offset_of_union!($union, $field), 0);
72 }
73
74 u
75 }};
76}
77