------- Additional Comments From sgk at troutmask dot apl dot washington dot
edu 2004-12-26 19:45 -------
Looks like you've found a bug in g77, and if you're reduction of NIST's 110
test is correct, then NIST also has the same bug. Here follows my digging
into this problem.
>From the Fortran 77 standard (ansi-x3dot9-1978-Fortran77.pdf)
4.4.1 Basic Real Constant
The form of a basic real constant is an optional sign, an integer part,
a decimal point, and a fractional part, in that order. Both the integer
part and the fractional part are strings of digits; either of these parts
may be omitted but not both. A basic real constant may be written with
more digits than a processor will use to approximate the value of the
constant. A basic real constant is interpreted as a decimal number.
13.5.9 Numeric Editing
The I, F, E, D, and G edit descriptors are used to specify input/output
of integer, real, double precision, and complex data. The following
general rules apply:
(1) On input, leading blanks are not significant. The interpretation
of blanks, other than leading blanks, is determined by a combination
of any BLANK= specifier and any BN or BZ blank control that is
currently in effect for the unit (13.5.8). Plus signs may be omitted.
A field of all blanks is considered to be zero.
It appears that the last sentence has been misinterpreted by g77 and NIST.
The wording from a May 2004 draft (04-007.pdf) of the newest standard is
R416 signed-real-literal-constant
is [ sign ] real-literal-constant
R417 real-literal-constant
is significand [ exponent-letter exponent ] [ kind-param ]
or digit-string exponent-letter exponent [ kind-param ]
R418 significand
is digit-string . [ digit-string ]
or . digit-string
R419 exponent-letter
is E
or D
R420 exponent
is signed-digit-string
10.6.1 Numeric editing
The I, B, O, Z, F, E, EN, ES, D, and G edit descriptors may be used to
specify the input/output of integer, real, and complex data. The
following general rules apply:
(1) On input, leading blanks are not significant. When the input field
is not an IEEE exceptional specification (10.6.1.2.1), the
interpretation of blanks, other than leading blanks, is determined
by the blank interpretation mode (10.7.6). Plus signs may be omitted.
A field containing only blanks is considered to be zero.
The first excerpt is the BNF of a real number. The second excerpt contains
the same misinterpreted sentence.
So, your output of 'E+00' in not a valid real number under either F77 or F2003
(and most likely F95). Secondly, the field you are reading is with the
E15.8 format, which is 15 characters wide, and this field does not contain only
blanks because you wrote E+00 into it.
If you change "write(19,'(A15)') 'E+00'" to the obvious blank-filled field,
gfortran does the right thing: "write(19,'(A15)') ' '"
--
steve
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19155
