On Mon, Apr 25, 2011 at 14:44, Jerry DeLisle <jvdeli...@frontier.com> wrote:
> On 04/25/2011 03:48 AM, Janne Blomqvist wrote:
>> Now, for one of the testcase changes:
>>
>> --- gcc/testsuite/gfortran.dg/char4_iunit_1.f03 (revision 172909)
>> +++ gcc/testsuite/gfortran.dg/char4_iunit_1.f03 (working copy)
>> @@ -24,11 +24,11 @@ program char4_iunit_1
>> write(string, *) .true., .false. , .true.
>> if (string .ne. 4_" T F T ") call
>> abort
>> write(string, *) 1.2345e-06, 4.2846e+10_8
>> - if (string .ne. 4_" 1.23450002E-06 42846000000.000000 ") call
>> abort
>> + if (string .ne. 4_" 1.234500019E-06 42846000000.000000 ") call
>> abort
>>
>> This looks wrong. For correctly rounded REAL(4) output, we need 9
>> significant digits, but here we print 10.
>>
>
> Well, I bumped it up for defaults based on pr48488 comment #2 shown below.
Yes, that comment in the PR is correct; to guarantee that a
binary->ascii->binary roundtrip preserves the original binary value
(with the default "round to nearest, break on even" rounding mode),
one must output at least {9, 17, 21, 36} significant digits for real
kinds 4, 8, 10, and 16, respectively (yes, I double-checked IEEE
754-2008 that this is indeed correct).
Since for the G edit descriptor d is equivalent to the number of
significant digits, AFAICS the write.c patch below is correct and the
bug must be elsewhere, no?
> Index: libgfortran/io/write.c
> ===================================================================
> --- libgfortran/io/write.c (revision 172909)
> +++ libgfortran/io/write.c (working copy)
> @@ -1432,8 +1432,8 @@ set_fnode_default (st_parameter_dt *dtp, fnode *f,
> switch (length)
> {
> case 4:
> - f->u.real.w = 15;
> - f->u.real.d = 8;
> + f->u.real.w = 16;
> + f->u.real.d = 9;
> f->u.real.e = 2;
> break;
> case 8:
> @@ -1442,13 +1442,13 @@ set_fnode_default (st_parameter_dt *dtp, fnode *f,
> f->u.real.e = 3;
> break;
> case 10:
> - f->u.real.w = 29;
> - f->u.real.d = 20;
> + f->u.real.w = 30;
> + f->u.real.d = 21;
> f->u.real.e = 4;
> break;
> case 16:
> - f->u.real.w = 44;
> - f->u.real.d = 35;
> + f->u.real.w = 45;
> + f->u.real.d = 36;
> f->u.real.e = 4;
> break;
> default:
>
--
Janne Blomqvist
