[Bug fortran/35036] illegal E format descriptor produces wrong output

["kargl at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from kargl at gcc dot gnu dot org  2008-01-31 02:24 -------
(In reply to comment #3)
> Subject: Re:  illegal E format descriptor produces wrong
>  output
> 
> Hi,
> 
> | ------- Comment #2 from kargl at gcc dot gnu dot org  2008-01-31 01:46
> -------
> | (In reply to comment #0)
> | > "E8.0" is an illegal format descriptor,
> | 
> | Can you cite from the Fortran 95 standard why this is illegal?
> 
> Good question :-)  Unfortunately, I don't have a Fortran 95 reference
> at hand, and so let me refer to the F77 standard:
> 
>   http://www.fortran.com/fortran/F77_std/rjcnf.html
> 
> 
> <QUOTE>
> 13.5.9.2.2 E and D Editing.
> The Ew.d, Dw.d, and Ew.dEe edit descriptors indicate that the external
> field occupies w positions, the fractional part of which consists of d
> digits, unless a scale factor greater than one is in effect, and the
> exponent part consists of e digits. The e has no effect on input. 
> 
> [. . .]
> 
> The scale factor k controls the decimal normalization (13.5.7). If -d
> < k <= 0, the output field contains exactly |k| leading zeros and d -
> |k| significant digits after the decimal point. If 0 < k < d + 2, the
> output field contains exactly k significant digits to the left of the
> decimal point and d - k + 1 significant digits to the right of the
> decimal point. Other values of k are not permitted.
> </QUOTE>
> 
> When d = 0, the only possible value for the scaling factor k is 1.
> Since "Other values of k are not permitted", you *must* use "1P"
> with d = 0, as "1PE8.0".  Q.E.D.
> 
> . . . I know this is a rather roundabout logic, and I'm not 100% sure,
> actually.  I'm curious.
> 
> Now, *if* "E8.0" is legal, what output should be generated for a value
> of 1e5 ?  "0.E5" ?

Actually, I think the 'correct' output might be 0.E6.

There is no restriction in F95 that d must be positive in Ew.d.
In 10.6.5.1, it clearly states that k = 0 at the beginning of 
execution of an input/output statement.  The wording you quote
above is (almost) identical to F95 language, so one could argue
that the -d < k <= 0 is true when d = 0 and k = 0.  Yes, it might
be a stupid interpretation, but then again the standard sometime
defies logic.

In any event, gfortran is definitely giving a bogus answer
of 0E+1, and your desired output of ******* is probably the
right thing to do.

jerry, any comments?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35036