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Commit | Line | Data |
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b7449926 | 1 | // run-pass |
0bf4aa26 | 2 | #![allow(dead_code)] |
3b2f2976 XL |
3 | |
4 | use std::mem; | |
5 | ||
6 | // Get around the limitations of CTFE in today's Rust. | |
7 | const fn choice_u64(c: bool, a: u64, b: u64) -> u64 { | |
8 | (-(c as i64) as u64) & a | (-(!c as i64) as u64) & b | |
9 | } | |
10 | ||
11 | const fn max_usize(a: usize, b: usize) -> usize { | |
12 | choice_u64(a > b, a as u64, b as u64) as usize | |
13 | } | |
14 | ||
15 | const fn align_to(size: usize, align: usize) -> usize { | |
16 | (size + (align - 1)) & !(align - 1) | |
17 | } | |
18 | ||
19 | const fn packed_union_size_of<A, B>() -> usize { | |
20 | max_usize(mem::size_of::<A>(), mem::size_of::<B>()) | |
21 | } | |
22 | ||
23 | const fn union_align_of<A, B>() -> usize { | |
24 | max_usize(mem::align_of::<A>(), mem::align_of::<B>()) | |
25 | } | |
26 | ||
27 | const fn union_size_of<A, B>() -> usize { | |
28 | align_to(packed_union_size_of::<A, B>(), union_align_of::<A, B>()) | |
29 | } | |
30 | ||
31 | macro_rules! fake_union { | |
32 | ($name:ident { $a:ty, $b:ty }) => ( | |
33 | struct $name { | |
34 | _align: ([$a; 0], [$b; 0]), | |
35 | _bytes: [u8; union_size_of::<$a, $b>()] | |
36 | } | |
37 | ) | |
38 | } | |
39 | ||
40 | // Check that we can (poorly) emulate unions by | |
41 | // calling size_of and align_of at compile-time. | |
42 | fake_union!(U { u16, [u8; 3] }); | |
43 | ||
44 | fn test(u: U) { | |
45 | assert_eq!(mem::size_of_val(&u._bytes), 4); | |
46 | } | |
47 | ||
48 | fn main() { | |
49 | assert_eq!(mem::size_of::<U>(), 4); | |
50 | assert_eq!(mem::align_of::<U>(), 2); | |
51 | } |