1 //! Miscellaneous minor utilities.
2 
3 #![allow(dead_code)]
4 #![allow(unused_macros)]
5 
6 use core::ffi::c_void;
7 use core::mem::{align_of, size_of};
8 use core::ptr::{null, null_mut, NonNull};
9 
10 /// Convert a `&T` into a `*const T` without using an `as`.
11 #[inline]
as_ptr<T>(t: &T) -> *const T12 pub(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]
as_mut_ptr<T>(t: &mut T) -> *mut T18 pub(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]
option_as_ptr<T>(t: Option<&T>) -> *const T24 pub(crate) const fn option_as_ptr<T>(t: Option<&T>) -> *const T {
25     match t {
26         Some(t) => t,
27         None => null(),
28     }
29 }
30 
31 /// Convert an `Option<&mut T>` into a possibly-null `*mut T`.
32 #[inline]
option_as_mut_ptr<T>(t: Option<&mut T>) -> *mut T33 pub(crate) fn option_as_mut_ptr<T>(t: Option<&mut T>) -> *mut T {
34     match t {
35         Some(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.
check_raw_pointer<T>(value: *mut c_void) -> Option<NonNull<T>>43 pub(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(value.cast())
51 }
52 
53 /// Create an array value containing all default values, inferring the type.
54 #[inline]
default_array<T: Default + Copy, const N: usize>() -> [T; N]55 pub(crate) fn default_array<T: Default + Copy, const N: usize>() -> [T; N] {
56     [T::default(); N]
57 }
58 
59 /// Create a union value containing a default value in one of its arms.
60 ///
61 /// The field names a union field which must have the same size as the union
62 /// itself.
63 macro_rules! default_union {
64     ($union:ident, $field:ident) => {{
65         let u = $union {
66             $field: Default::default(),
67         };
68 
69         // Assert that the given field initializes the whole union.
70         #[cfg(test)]
71         unsafe {
72             let field_value = u.$field;
73             assert_eq!(
74                 core::mem::size_of_val(&u),
75                 core::mem::size_of_val(&field_value)
76             );
77             const_assert_eq!(memoffset::offset_of_union!($union, $field), 0);
78         }
79 
80         u
81     }};
82 }
83