A review of endianness bugs in Qt, and how they were fixed

Re:A review of endianness bugs in Qt, and how they were fixed by askee on Saturday January 02, 2021 @09:28AM (#25613019)

It's also about performance. The snippet assumes the byte order of the buffer or byte stream is little endian so only covers two of four cases. If you want to read a little-endian byte stream on a big-endian machine, of course you need swapping. But, considering portability, if that byte stream had been written by the big-endian machine before (or came directly from network) it would be in big-endian ordering and swapping would be wrong.

Assuming LE ordering on the writer side, you would need to swap again on a BE machine. Usually, however, you want to store in your target byte order, though. One could argue this is irrelevant as long as the memory doesn't leave your application, of course. Yet, by explicitly having macros _to_cpu, _to_be, _to_le and so on you make all of this explicit.

[ Parent | on HN ]

Re:A review of endianness bugs in Qt, and how they were fixed by sgerenser on Saturday January 02, 2021 @02:30PM (#25615646)

The snippet assumes the data being read is little endian, yes. You can make a different snippet if you want to read big endian. You use an equivalent snippet for the writing side, and boom. You never need any #ifdefs in those functions. Is it actually better than using functions like you describe? Maybe. A part of me does love the elegance of using the exact same code on any platform regardless of the native byte order. This construct was suggested/encouraged by Rob Pike: https://commandcenter.blogspot.com/2012/04/byte-order-fallac...

[ Parent | on HN ]