1const std = @import("std");
 2const builtin = @import("builtin");
 3const assert = std.debug.assert;
 4const expectEqual = std.testing.expectEqual;
 5const native_endian = builtin.cpu.arch.endian();
 6
 7test "packed struct explicit backing integer" {
 8    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
 9    if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
10
11    const S1 = packed struct { a: u8, b: u8, c: u8 };
12
13    const S2 = packed struct(i24) { d: u8, e: u8, f: u8 };
14
15    const S3 = packed struct { x: S1, y: S2 };
16    const S3Padded = packed struct(u64) { s3: S3, pad: u16 };
17
18    try expectEqual(48, @bitSizeOf(S3));
19    try expectEqual(@sizeOf(u48), @sizeOf(S3));
20
21    try expectEqual(3, @offsetOf(S3, "y"));
22    try expectEqual(24, @bitOffsetOf(S3, "y"));
23
24    if (native_endian == .little) {
25        const s3 = @as(S3Padded, @bitCast(@as(u64, 0xe952d5c71ff4))).s3;
26        try expectEqual(@as(u8, 0xf4), s3.x.a);
27        try expectEqual(@as(u8, 0x1f), s3.x.b);
28        try expectEqual(@as(u8, 0xc7), s3.x.c);
29        try expectEqual(@as(u8, 0xd5), s3.y.d);
30        try expectEqual(@as(u8, 0x52), s3.y.e);
31        try expectEqual(@as(u8, 0xe9), s3.y.f);
32    }
33
34    const S4 = packed struct { a: i32, b: i8 };
35    const S5 = packed struct(u80) { a: i32, b: i8, c: S4 };
36    const S6 = packed struct(i80) { a: i32, b: S4, c: i8 };
37
38    const expectedBitSize = 80;
39    const expectedByteSize = @sizeOf(u80);
40    try expectEqual(expectedBitSize, @bitSizeOf(S5));
41    try expectEqual(expectedByteSize, @sizeOf(S5));
42    try expectEqual(expectedBitSize, @bitSizeOf(S6));
43    try expectEqual(expectedByteSize, @sizeOf(S6));
44
45    try expectEqual(5, @offsetOf(S5, "c"));
46    try expectEqual(40, @bitOffsetOf(S5, "c"));
47    try expectEqual(9, @offsetOf(S6, "c"));
48    try expectEqual(72, @bitOffsetOf(S6, "c"));
49}