Re: [patch, libgfortran] PR48906 Wrong rounding results with -m32

[jerry DeLisle <jvdelisle@charter.net>]

On 06/11/2011 12:23 AM, Thomas Henlich wrote:
>> I don't agree with this; with the patch we now output 10 significant
>> digits, whereas 9 is sufficient for a binary->ascii->binary roundtrip.
>> So please retain the "reduce d by one when E editing is used" thing
>> for list format and G0. This is just a side effect of using 1PGw.d
>> format for list format and G0 in order to avoid duplicating code, but
>> we don't need to follow this particular craziness that is due to how
>> the scale factor is specified in the standard.
>
> I hadn't noticed this, but I agree with Janne.
>
> It should be easy to implement:
>
> After the switch between F and E editing, we just need to shift the
> decimal point and decrement the exponent. No new rounding is required,
> because we keep the number of significant digits.
>

Our default formats for kind=4 are:

static void
set_fnode_default (st_parameter_dt *dtp, fnode *f, int length)
{
   f->format = FMT_G;
   switch (length)
     {
     case 4:
       f->u.real.w = 16;
       f->u.real.d = 9;
       f->u.real.e = 2;
       break;

This was established as solution to PR48488 where we had two choices for 
selecting the significant digits. Nine significant digits was established as a 
requirement to guarantee round trip in all cases. The char4_iunit_1.f03 test 
case was revised because after we corrected the formatting in PR48906, it 
started to fail and I observed the test case was looking for the wrong number of 
significant digits.

Based on this, I would suggest we leave it as I have it, which is correct.

Jerry