This is the mail archive of the
mailing list for the Cygwin project.
Re: 1.7.8: Fortran I/O rounding inaccuracy
On Mon, Mar 7, 2011 at 10:39 AM, Thomas Henlich wrote:
> I found the following bug in cygwin 1.7.8 on Windows XP:
> Fortran I/O rounding truncates the result after a certain number of
> digits. The following program:
> write(*, '(f35.32)') 0.14285714285714285d0
> gives this output:
> The expected output is:
> This is in violation of the Fortran 2008 standard which demands:
I doubt our compiler is Fortran 2008 compliant, as at maximum it will
be Fortran 2003
> 10.7.2.3.7 I/O rounding mode
> 2. In what follows, the term "decimal value" means the exact decimal number as
> given by the character string, while the term "internal value" means the number
> actually stored in the processor. ?For example, in dealing with the decimal
> constant 0.1, the decimal value is the mathematical quantity 1/10, which has no
> exact representation in binary form. ?Formatted output of real data involves
> conversion from an internal value to a decimal value; formatted input involves
> conversion from a decimal value to an internal value.
> 3. ?When the I/O rounding mode is UP, the value resulting from conversion shall
> be the smallest representable value that is greater than or equal to the
> original value. When the I/O rounding mode is DOWN, the value resulting
> from conversion shall be the largest representable value that is less than or
> equal to the original value. ...
> Applied to the example this means, 0.14285714285714284921269268124888
> is the largest representable
> (with 32 decimal digits) value that is less than the original value (binary
> 1.001001001001001001001001001001001001001001001001001 * 2^-3 = decimal
> 0.1428571428571428492126926812488818...), but
> 0.14285714285714284921269000000000 is NOT.
> The problem seems limited to the Fortran language, because the C call
> printf("%35.32f\n", 0.14285714285714285) prints the expected result:
> Problem reports: ? ? ? http://cygwin.com/problems.html
> FAQ: ? ? ? ? ? ? ? ? ? http://cygwin.com/faq/
> Documentation: ? ? ? ? http://cygwin.com/docs.html
> Unsubscribe info: ? ? ?http://cygwin.com/ml/#unsubscribe-simple
Have you tested gfortran 4.3 on other platform ?
Problem reports: http://cygwin.com/problems.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple