mirror of https://github.com/rust-lang/rust
60 lines
1.7 KiB
Rust
60 lines
1.7 KiB
Rust
//@ run-pass
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#![feature(const_ptr_sub_ptr)]
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#![feature(ptr_sub_ptr)]
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struct Struct {
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field: (),
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}
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#[repr(C)]
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struct Struct2 {
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data: u8,
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field: u8,
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}
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pub const OFFSET: usize = {
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let uninit = std::mem::MaybeUninit::<Struct>::uninit();
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let base_ptr: *const Struct = &uninit as *const _ as *const Struct;
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// The following statement is UB (taking the address of an uninitialized field).
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// Const eval doesn't detect this right now, but it may stop compiling at some point
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// in the future.
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let field_ptr = unsafe { &(*base_ptr).field as *const () as *const u8 };
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let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
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offset as usize
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};
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pub const OFFSET_2: usize = {
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let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
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let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
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let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
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let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
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offset as usize
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};
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pub const OVERFLOW: isize = {
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let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
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let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
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let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
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unsafe { (base_ptr as *const u8).offset_from(field_ptr) }
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};
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pub const OFFSET_EQUAL_INTS: isize = {
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let ptr = 1 as *const u8;
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unsafe { ptr.offset_from(ptr) }
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};
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pub const OFFSET_UNSIGNED: usize = {
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let a = ['a', 'b', 'c'];
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let ptr = a.as_ptr();
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unsafe { ptr.add(2).sub_ptr(ptr) }
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};
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fn main() {
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assert_eq!(OFFSET, 0);
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assert_eq!(OFFSET_2, 1);
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assert_eq!(OVERFLOW, -1);
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assert_eq!(OFFSET_EQUAL_INTS, 0);
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assert_eq!(OFFSET_UNSIGNED, 2);
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}
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