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Diffstat (limited to 'third_party/rust/memoffset-0.5.6/src/offset_of.rs')
| -rw-r--r-- | third_party/rust/memoffset-0.5.6/src/offset_of.rs | 212 |
1 files changed, 212 insertions, 0 deletions
diff --git a/third_party/rust/memoffset-0.5.6/src/offset_of.rs b/third_party/rust/memoffset-0.5.6/src/offset_of.rs new file mode 100644 index 0000000000..bb2bce1c2f --- /dev/null +++ b/third_party/rust/memoffset-0.5.6/src/offset_of.rs @@ -0,0 +1,212 @@ +// Copyright (c) 2017 Gilad Naaman +// +// Permission is hereby granted, free of charge, to any person obtaining a copy +// of this software and associated documentation files (the "Software"), to deal +// in the Software without restriction, including without limitation the rights +// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +// copies of the Software, and to permit persons to whom the Software is +// furnished to do so, subject to the following conditions: +// +// The above copyright notice and this permission notice shall be included in all +// copies or substantial portions of the Software. +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +// SOFTWARE. + +/// Macro to create a local `base_ptr` raw pointer of the given type, avoiding UB as +/// much as is possible currently. +#[cfg(maybe_uninit)] +#[macro_export] +#[doc(hidden)] +macro_rules! _memoffset__let_base_ptr { + ($name:ident, $type:path) => { + // No UB here, and the pointer does not dangle, either. + // But we have to make sure that `uninit` lives long enough, + // so it has to be in the same scope as `$name`. That's why + // `let_base_ptr` declares a variable (several, actually) + // instead of returning one. + let uninit = $crate::mem::MaybeUninit::<$type>::uninit(); + let $name: *const $type = uninit.as_ptr(); + }; +} +#[cfg(not(maybe_uninit))] +#[macro_export] +#[doc(hidden)] +macro_rules! _memoffset__let_base_ptr { + ($name:ident, $type:path) => { + // No UB right here, but we will later dereference this pointer to + // offset into a field, and that is UB because the pointer is dangling. + let $name = $crate::mem::align_of::<$type>() as *const $type; + }; +} + +/// Macro to compute the distance between two pointers. +#[cfg(feature = "unstable_const")] +#[macro_export] +#[doc(hidden)] +macro_rules! _memoffset_offset_from { + ($field:expr, $base:expr) => { + // Compute offset, with unstable `offset_from` for const-compatibility. + // (Requires the pointers to not dangle, but we already need that for `raw_field!` anyway.) + unsafe { ($field as *const u8).offset_from($base as *const u8) as usize } + }; +} +#[cfg(not(feature = "unstable_const"))] +#[macro_export] +#[doc(hidden)] +macro_rules! _memoffset_offset_from { + ($field:expr, $base:expr) => { + // Compute offset. + ($field as usize) - ($base as usize) + }; +} + +/// Calculates the offset of the specified field from the start of the struct. +/// +/// ## Examples +/// ``` +/// #[macro_use] +/// extern crate memoffset; +/// +/// #[repr(C, packed)] +/// struct Foo { +/// a: u32, +/// b: u64, +/// c: [u8; 5] +/// } +/// +/// fn main() { +/// assert_eq!(offset_of!(Foo, a), 0); +/// assert_eq!(offset_of!(Foo, b), 4); +/// } +/// ``` +#[macro_export(local_inner_macros)] +macro_rules! offset_of { + ($parent:path, $field:tt) => {{ + // Get a base pointer (non-dangling if rustc supports `MaybeUninit`). + _memoffset__let_base_ptr!(base_ptr, $parent); + // Get field pointer. + let field_ptr = raw_field!(base_ptr, $parent, $field); + // Compute offset. + _memoffset_offset_from!(field_ptr, base_ptr) + }}; +} + +#[cfg(test)] +mod tests { + #[test] + fn offset_simple() { + #[repr(C)] + struct Foo { + a: u32, + b: [u8; 2], + c: i64, + } + + assert_eq!(offset_of!(Foo, a), 0); + assert_eq!(offset_of!(Foo, b), 4); + assert_eq!(offset_of!(Foo, c), 8); + } + + #[test] + #[cfg_attr(miri, ignore)] // this creates unaligned references + fn offset_simple_packed() { + #[repr(C, packed)] + struct Foo { + a: u32, + b: [u8; 2], + c: i64, + } + + assert_eq!(offset_of!(Foo, a), 0); + assert_eq!(offset_of!(Foo, b), 4); + assert_eq!(offset_of!(Foo, c), 6); + } + + #[test] + fn tuple_struct() { + #[repr(C)] + struct Tup(i32, i32); + + assert_eq!(offset_of!(Tup, 0), 0); + assert_eq!(offset_of!(Tup, 1), 4); + } + + #[test] + fn path() { + mod sub { + #[repr(C)] + pub struct Foo { + pub x: u32, + } + } + + assert_eq!(offset_of!(sub::Foo, x), 0); + } + + #[test] + fn inside_generic_method() { + struct Pair<T, U>(T, U); + + fn foo<T, U>(_: Pair<T, U>) -> usize { + offset_of!(Pair<T, U>, 1) + } + + assert_eq!(foo(Pair(0, 0)), 4); + } + + #[test] + fn test_raw_field() { + #[repr(C)] + struct Foo { + a: u32, + b: [u8; 2], + c: i64, + } + + let f: Foo = Foo { + a: 0, + b: [0, 0], + c: 0, + }; + let f_ptr = &f as *const _; + assert_eq!(f_ptr as usize + 0, raw_field!(f_ptr, Foo, a) as usize); + assert_eq!(f_ptr as usize + 4, raw_field!(f_ptr, Foo, b) as usize); + assert_eq!(f_ptr as usize + 8, raw_field!(f_ptr, Foo, c) as usize); + } + + #[cfg(feature = "unstable_const")] + #[test] + fn const_offset() { + #[repr(C)] + struct Foo { + a: u32, + b: [u8; 2], + c: i64, + } + + assert_eq!([0; offset_of!(Foo, b)].len(), 4); + } + + #[cfg(feature = "unstable_const")] + #[test] + fn const_fn_offset() { + const fn test_fn() -> usize { + #[repr(C)] + struct Foo { + a: u32, + b: [u8; 2], + c: i64, + } + + offset_of!(Foo, b) + } + + assert_eq!([0; test_fn()].len(), 4); + } +} |