Default format for Float128

[Steve Kargl]

On Wed, Sep 01, 2010 at 08:54:32PM -0700, Jerry DeLisle wrote:
> Hi all,
> 
> With FX help I managed to get a build working with the libquad support. 
> (allowing me to test)
> 
> The following program illustrates some default formatting.
> 
> program test_quad
>   real(16) :: num1, num2, num3
>   real(8) :: tmp
> 
>   num1 = 23.456_16 / 3.3_16
>   num2 = 42.86_16
>   num3 = -5.2562-16
>   tmp = num1 + num2 + num3
>   print *, "1234567890123456789012345678901234567890"
>   write(*,*) tmp
>   write(*,*) num1
>   write(*,*) num2
>   write(*,*) num3
>   write(*,*) num1 + num2 + num3
>   print *, "1234567890123456789012345678901234567890"
>   print *, 1.0_16/3.0_16
>   print *, 1.0_10/3.0_10
>   print *, 1.0_8/3.0_8
>   print *, 1.0_4/3.0_4
> end program test_quad
> 
> Which on my system, results in:
> 
> $ ./a.out
>  1234567890123456789012345678901234567890
>    28.711679904822148
>    7.1078787878787878787879000000000000
>    42.860000000000000000000000000000000
>   -21.256198883056640625000000000000000
>    28.711679904822147253788000000000000
>  1234567890123456789012345678901234567890
>   0.33333333333333333333333000000000000
>   0.33333333333333333334
>   0.33333333333333331
>   0.33333334
> 
> There appears to be a lot of excess width here.  If I modify write.c with 
> this:
> 
> Index: write.c
> ===================================================================
> --- write.c     (revision 163712)
> +++ write.c     (working copy)
> @@ -1447,8 +1447,8 @@
>        f->u.real.e = 4;
>        break;
>      case 16:
> -      f->u.real.w = 44;
> -      f->u.real.d = 35;
> +      f->u.real.w = 32;
> +      f->u.real.d = 23;

Are you sure this is correct?  

troutmask:sgk[205] cat j.f90
real(16) x
print *, precision(x), digits(x)
end

troutmask:sgk[206] gfc4x -o z j.f90
troutmask:sgk[207] ./z
          33         113

There are 33 decimal digits of precision.
Shouldn't the default format be something
like s0.[33 digits]ES00 where s and S are
+ or -.  This gives w = 40 and d = 33.

Of course, I could be wrong about what real.[wd]
mean.

-- 
Steve