Re: struct ldieee should be packed

[Craig Howland <howland at LGSInnovations dot com>]

On 01/30/2016 01:56 AM, Shoichi Sakon wrote:
> Hello,
>
> The following test program prints 1.0 instead of -1.0.
> -------------------------------------
> #include <stdio.h>
> int main() {
>          double x = -1.0;
>          printf("%f\n",x);
> 	return 0;
> }
> -------------------------------------
>
> I believe the cause of the problem is the struct ldieee
> defined in newlib/libc/stdio/vfieeefp.h is not "packed",
> and in the function cvt in newlib/libc/stdio/vfieeefp.h
> ld.ieee.sign does not get the proper sign.
>
> When I change all the definitions of
>   struct ldieee
> to
>   struct __attribute__ ((__packed__)) ldieee
> I can get the right result at the test program.
What compiler version and platform are you targeting?
Can you try the following as an experiment?  instead of adding packed (which is 
non-standard), merge the bitfields to be under a single element instead of 
separate ones for you entry of interest. For example, change
#if LDBL_MANT_DIG == 24
 struct ldieee
 {
   unsigned manh:23;
   unsigned exp:8;
   unsigned sign:1;
 };

to

 {
   unsigned manh:23,
                  exp:8,
                  sign:1;
 };

Craig