Re: what you can do with bitfields

On 11/30/2024 9:50 AM, fir wrote:

Lawrence D'Oliveiro pisze:

On Thu, 28 Nov 2024 14:39:43 +0100, fir wrote:
>

i use them but i never fully chcked what i can do with them ...

>
One problem with C is that bitfields can only have static offsets and
sizes. If these were dynamic, you could express much more powerful
manipulations more conveniently than with shifting and masking.
>

what do you mean?
i must check hovever how this static work at all.. i used them
and not so rarely but only simple cases usually for solo bit flags

Most common way to do bit flags:
   #define WHATEVER_FLAG1  0x0001
   #define WHATEVER_FLAG2  0x0002
   ...
And:
   if(flags&WHATEVER_FLAG1)
     { ... }
Though, for larger bit-flags, on some targets it may be more efficient to do:
   if((flags>>WHATEVER_FLAG43_SHR)&1)
     { ... }
For example, RISC-V, where shift-right and mask will use fewer instructions than constant-load and mask.
...