Re: Desire to allocate bit in DT_PARM bitmask for DEC FORMAT compatibility purposes

[Jerry DeLisle <jvdelisle@charter.net>]

On 03/23/2018 01:38 AM, Jakub Jelinek wrote:
> On Fri, Mar 23, 2018 at 09:12:21AM +0100, Jakub Jelinek wrote:
>>> I have some philosophical questions.
>>>
>>> 1) Why do you want 15, 7, 2? Why is this so critical?
>>
>> Because that is what all those compilers document and agree on.
>> See e.g.
>> https://software.intel.com/en-us/node/678750#32937290-265D-4805-B2B7-4E78F6AAD0D8
>> for Intel documentation, I'm sure Jeff has links to other documentations.
> 
> BTW, it seems libgfortran already has a similar extension, at least my
> reading of the standards (checked 97 and 2003) is that for Lw the standard
> doesn't allow omitting the width, but we allow that as extension:
>            else
>              {
>                fmt->saved_token = t;
>                notify_std (&dtp->common, GFC_STD_GNU,
>                            "Positive width required with L descriptor");
>              }
>            fmt->value = 1;       /* Default width */
> (and sadly different from what Intel Fortran does, because it uses 2).
> Wonder about other compilers, if they all agree on 2, perhaps we should
> behave above differently based on the new bit?
> 
> 	Jakub
> 

Putting on my "practical" hat, if an application writes large volumes of 
data to a formatted file as a means of intermediate storage and then 
reads it back in for further processing and uses tab specifiers to 
position the read to get at a certain field, they would be screwed with 
gfortran.

I agree that with so many other compilers doing this, we should do so.

The warning we issue should state that there is a loss of precision in 
formatted file I/O.

Also I wonder if we should test the bit in set_fnode_default and do the 
changes there so they are all in one place and all the other default 
formatting should just work. For example, write(6, *) would use the 
smaller widths if the flag is set.

Also, could someone point me to a a real good example of this kind of 
DEC Fortran code so I can get a better feel for this.

Regards,

Jerry