40 lines
993 B
Rust
40 lines
993 B
Rust
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// run-pass
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#![feature(layout_for_ptr)]
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use std::mem;
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#[repr(packed(4))]
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struct Slice([u32]);
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#[repr(packed(2), C)]
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struct PackedSized {
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f: u8,
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d: [u32; 4],
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}
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#[repr(packed(2), C)]
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struct PackedUnsized {
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f: u8,
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d: Slice,
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}
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impl PackedSized {
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fn unsize(&self) -> &PackedUnsized {
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// We can't unsize via a generic type since then we get the error
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// that packed structs with unsized tail don't work if the tail
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// might need dropping.
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let len = 4usize;
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unsafe { mem::transmute((self, len)) }
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}
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}
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fn main() { unsafe {
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let p = PackedSized { f: 0, d: [1, 2, 3, 4] };
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let p = p.unsize() as *const PackedUnsized;
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// Make sure the size computation correctly adds exact 1 byte of padding
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// in front of the `d` field.
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assert_eq!(mem::size_of_val_raw(p), 1 + 1 + 4*4);
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// And likewise for the offset computation.
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let d = std::ptr::addr_of!((*p).d);
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assert_eq!(d.cast::<u32>().read_unaligned(), 1);
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} }
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