Re: [Tinycc-devel] question about bit-fields

[grischka]

Didier Barvaux wrote:
> On a structure such as:
>   struct mystruct1
>   {
>      unsigned int mystruct1_foo:4;
>      unsigned int mystruct1_bar:4;
>      uint8_t mystruct1_other;
>      uint16_t mystruct1_other2;
>   };
>
> The 2 first fields uses 1 byte with GCC/Clang while they use
> sizeof(unsigned int) bytes with TCC. GCC/Clang pack the bit fields on
> the smaller type available. So, sizeof(struct mystruct1) = 4 with
> GCC/Clang and sizeof(struct mystruct1) = 8 with TCC.

I tried your "bitfield.c" test with GCC and it failed on the 2nd
assertion.  Hm ...

--- grischka

> My program (and probably many others, as the struct iphdr for IPv4
> header defined by the GNU libc is defined that way) relies on this
> behaviour. That's why I created the patch. It packs bit fields "the way
> GCC does". If you got a better description, I'll be happy to change
> it :)