On 04/11/11 11:35, Kjell Rilbe wrote: > Den 2011-04-11 09:19 skrev Alex Peshkoff såhär: >> I'm far not sure everything is so fine with that structure/class. Look here: >> unsigned >> blrLength; >> >> const unsigned char* blr; >> Pointer (8-bytes object) is placed after integer (4-bytes object). C >> language has a requirement to align it on 8-bytes boundary, but what >> about others? I't quite possible that some other language will try to >> save memory. The result is obvious - segfault when we use such structure. > 1. This is a doc issue more than anything. There's always a workaround, > e.g. insering dummy fields in a language that uses "packed" > recs/structs. Just make sure you document the binary format complete > with alignment/padding.
That's possible, I think. But not too good. The main disadvantage that this layout may probably differ for different hardware. And what - with every new port rewrite/review a piece of documentation? > 2. If I'm not mistaken most languages support a "packed" directive that > tells the compiler to not align/pad the struct. Delphi does. But I doubt > it's possible to do the other way around: tell a compiler to pad/align > to N bytes. So, perhaps the most compatible way is to use packed structs > everywhere. That's impossible at least for RISC machines. > On the other hand, this will probably induce a performance > hit - that's why alignment is used at all. Yes, it's known fact that some intel CPUs have serious performance hit when working with misaligned data. ------------------------------------------------------------------------------ Xperia(TM) PLAY It's a major breakthrough. An authentic gaming smartphone on the nation's most reliable network. And it wants your games. http://p.sf.net/sfu/verizon-sfdev Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
