[cc65-devel] Fwd: Re: bitfields again

[Vorsichtphysiker <vor...@gm...>]

-------- Forwarded Message --------
Subject: 	Re: [cc65-devel] bitfields again
Date: 	Sat, 9 Dec 2017 23:18:31 +0100
From: 	Vorsichtphysiker <vor...@gm...>
To: 	Greg King <gre...@ve...>



No, sorry.

Here is my updated program. This has been compiled without -O switch, to
be sure.

It outputs 0 1 0 1 0 1 0 instead of 0 1 0 2 0 4 0, like gcc does.


#include <stdio.h>
#include <stdlib.h>

typedef union{
     unsigned int bf;

     struct{
         unsigned int a:1;
         unsigned int b:1;
         unsigned int c:1;
     };
} bitfield_t;

int main()
{
     bitfield_t bitfield = {0};


     printf("Bitfield: %u\n", bitfield.bf);
     bitfield.a = bitfield.a ^ 1;
     printf("a=1: %u\n", bitfield.bf);
     bitfield.a = bitfield.a ^1;
     printf("a=0: %u\n\n", bitfield.bf);

     bitfield.b = bitfield.b ^1;
     printf("b=1: %u\n", bitfield.bf);
     bitfield.b = bitfield.b ^ 1;
     printf("b=0: %u\n\n", bitfield.bf);

     bitfield.c = bitfield.c ^1;
     printf("c=1: %u\n", bitfield.bf);
     bitfield.c = bitfield.c ^ 1;
     printf("c=0: %u\n\n", bitfield.bf);
     return 0;
}




On 07.12.2017 21:42, Greg King wrote:
> On 2017-12-05 10:31 AM, Stefan wrote:
>> Sorry to tell, but the workaround using x = 1-x does not work, too.
>> All what is left as a workaround is using conditionals to toggle 
>> bitfield;
>> or, manually read the value, store it in a variable, toggle that 
>> variable, and
>> then set it again. I don't think that would be an acceptable 
>> alternative.
>
> Does "expanding" the ^= operator work in your program?
>
> myBF.asBF.f3 = myBF.asBF.f3 ^ 1;
>
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