Bitwise portable issue

[apple-ouyang]

I found a stackoverflow post saying that the bitfield is not portable. The only portable code is using bit-wise operators. So should we change to bit-wise operators? @i404788

[i404788]

It seems to be implementation-defined by the C standard although I believe it's consistent across the major compilers that support packed bitfields, I can do some tests for that. For little-endian machines a difference does need to be made (http://mjfrazer.org/mjfrazer/bitfields/), however that is also needed when using bit-wise operators (if the deltas are transferred across platforms).

[i404788]

OSX:

• GNU GCC-11 & Apple Clang 12 use the same layout. Linux:
• LLVM clang 12 & GNU GCC-10 use the same layout
• GNU GCC-6 & GNU GCC-10 use the same layout
• MinGW32 has same layout when using -mno-ms-bitfields (seems like microsoft might implement it differently)

To test:

• [x] GNU GCC
  • [x] 6
  • [x] 11
• [x] Apple Clang
  • [x] 12
• [x] MSVC (https://godbolt.org/z/c4cj4jzMs)
• [x] MinGW GCC
• [x] LLVM Clang
  • [x] 12

[apple-ouyang]

I look forward to seeing your test results

[i404788]

I've completed testing, with some minor changes it does work across all compilers listed above (check the msvc gobolt link for the final code). I'll create a pull request later