Struct 对齐与 Padding

  编译:成功
  运行(退出码 0):
      u8             size  1  align  1
      u16            size  2  align  2
      u32            size  4  align  4
      u64            size  8  align  8
      u128           size 16  align 16
      f64            size  8  align  8
      char           size  4  align  4
      bool           size  1  align  1
      usize          size  8  align  8
      &u8            size  8  align  8
      (u8, u32)      size  8  align  4
      [u16; 3]       size  6  align  2
      S1             size  2  align  1
      S2             size  8  align  4
      S3             size 16  align  8
      S4             size  8  align  2

  type: `MixedC`: 32 bytes, alignment: 8 bytes
      field `.a`: 1 bytes
      padding: 7 bytes
      field `.b`: 8 bytes, alignment: 8 bytes
      field `.c`: 1 bytes
      padding: 3 bytes
      field `.d`: 4 bytes, alignment: 4 bytes
      field `.e`: 2 bytes
      end padding: 6 bytes
  type: `Mixed`: 16 bytes, alignment: 8 bytes
      field `.b`: 8 bytes
      field `.d`: 4 bytes
      field `.e`: 2 bytes
      field `.a`: 1 bytes
      field `.c`: 1 bytes

  编译:成功
  运行(退出码 0):
    size_of::<S>() = 8,元素间距 = 8 和 8
    每个元素地址 % align(4) = 0 0 0
    一个 u8 数组里偏移 0..8 的位置,按 u32 对齐的占 2 个,不对齐的占 6 个

  编译:成功
  运行(退出码 0):
    对齐的 u32 读取(偏移 0):       每次 0.45 ns
    不对齐的 u32 读取(偏移 1):     每次 0.46 ns(read_unaligned,结果不同是因为读的字节不同:106686713290400000 对 106113205749200000)
  编译:成功
  运行(退出码 -6):
    read_unaligned 读偏移 1 的 u32 = 0x5040302
    
    thread 'main' (7305060) panicked at <实验目录>/src/u113e.rs:6:22:
    misaligned pointer dereference: address must be a multiple of 0x4 but is 0x16b41a7e5
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
    thread caused non-unwinding panic. aborting.