Am 09.12.2013 21:08, schrieb Jonathan Nieder:
> Karsten Blees wrote:
>> GCC supports __packed__ as of 2.3 (1992), so any other compilers
>> that copied the __attribute__ feature probably won't complain.
> Alas, it looks like HP C doesn't support __packed__ (not that I
> care much about HP C):

Thanks for the link

> Maybe a macro expanding to __attribute__((aligned(1))) on the fields
> would work?  The same macro could expand to __declspec(align(1)) in
> the MSVC build.

But alignment is not the same as packing. We still want the structure to be 
8-byte aligned (i.e. variables of the type should start at 8-byte boundaries). 
We just don't want the size of the structure to be padded to a multiple of 8, 
so that we can extend it without penalty. (Besides, __attribute__((aligned)) / 
__declspec(align) can only _increase_ the alignment, so aligned(1) would have 
no effect).

Googling some more, I believe the most protable way to achieve this via 
'compiler settings' is

 #pragma pack(push)
 #pragma pack(4)
 struct hashmap_entry {
   struct hashmap_entry *next;
   unsigned int hash;
 #pragma pack(pop)

This is supported by at least GCC, MSVC and HP (see your link). The downside is 
that we cannot use macros (in git-compat-util.h) to emit #pragmas. But we 
wouldn't have to, as compilers aren't supposed to barf on unknown #pragmas.

However, considering the portability issues, the macro solution (injecting just 
the two fields instead of a struct) becomes more and more attractive in my 


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