[Bug libfortran/24685] real(16) formatted input is broken for huge values

["sje at cup dot hp dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #12 from sje at cup dot hp dot com  2006-03-15 16:44 -------
At least on IA64, I don't think there is a way to make this test work.  I tried
a change similar to yours.  I also changed the setting of ndigits (uses the
magic number 27 in a couple of places), changed the number 31 in the sprintf
statement and the number 32 (buffer size) in the snprintf statement.  This
fixed the LDBL_MAX problem but the test still failed on the LDBL_MIN part of
the test.

The attached C program fails on IA64 because the printf rounds the last digit
of MIN_LDBL down when it prints it and so it can't be read back in.  The basic
problem is that LDBL_MAX and LDBL_MIN (or for that matter DBL_MIN and DBL_MAX)
cannot be represented exactly in decimal form so printf has to do some rounding
that may make the process non-reversable when trying to go back via strtod or
strtold.  I looked to see if there was a float or double version of this test
and I didn't find one, if there was one I think it would fail on some platforms
because the write/read sequence is not gauranteed to return the original value
due to possible rounding during the writing and/or reading process.

#include <stdio.h>
#include <float.h>
#include <errno.h>

main()
{
        char buffer[64];
        long double x = LDBL_MIN;
        sprintf(buffer, "%63.40Le", x);
        printf("==%s==\n", buffer);
        errno = 0;
        x = strtold(buffer, 0);
        printf("errno = %d\n", errno);
}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24685