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Date:	Wed, 13 Mar 2013 21:02:40 +0100
From:	Juan Manuel Guerrero <juan DOT guerrero AT gmx DOT de>
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To:	djgpp-workers AT delorie DOT com
Subject:	Re: Printing sign of NaN.
References:	<201303111624 DOT r2BGO6lZ014367 AT dexter DOT ludd DOT ltu DOT se>
In-Reply-To:	<201303111624.r2BGO6lZ014367@dexter.ludd.ltu.se>
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Reply-To:	djgpp-workers AT delorie DOT com

Am 11.03.2013 17:24, schrieb Martin Strömberg:
[snip]

 > Now over to the NaNs.
 >
 > Just because Linux's libc does one thing, it's not automatically the
 > right/best/whatever way to do it.
 >
 > While the sign of the NaN might help to diagnose what went wrong it's
 > not enough. Preferably _all_ the bits of the NaN should be presented.
 >
 > IIRC, that is allowed, but it been a while since I was messing with
 > this. I thought I did it for DJGPP, but I can't see anything in the
 > code about that, or perhaps I'm looking at the wrong places. It can be
 > that I never finished it so I didn't send it. Or perhaps it was just
 > for my own debugging I was messing with NaNs.
 >
 > Anyway, IIRC you are allowed to print "NaN(some representation of the
 > bits of the NaN)" when you print a NaN as long as your *scanf() accept
 > it as well.
 >
 > So I suggest if you really want to make the printing of NaNs better do
 > that.
 >
 > My plan was to just dump the bits of the whole floating point number
 > (just be make implementing it easy), something like (pseudocode)
 >
 > print_double(double d) {
 >   if( isnan(d) ) {
 >     printf("NaN(0x%x)", (unsigned long long)d);
 >   } else {
 >     printf("%d", d);
 >   }
 > }
 >
 > scanf_double(char string, double *d_p) {
 >   unsinged long long ull;
 >   if( 1 == sscanf(string, "NaN(%llx)", &ull ) {
 >     ull |= 0x<whatever bits that must be set to make a NaN>;
 >     *d_p = *(double *)&ull;
 >   } elsif( 1 == sscanf(string, "nan(%llx)", &ull ) {
 >     /* Same as above. */
 >   } elsif( X == sscanf(string, <more variations of NaN> ...) {
 >     ...
 >   }
 > }
 >
 > With that you can forget about the sign as you'll see that by looking
 > at the bit patterns. And it sure is much better than what you're
 > trying to copy from Linux's libc.
 >
 > I just don't see the point of printing only the sign and not the other
 > interesting bits (the mantissa IIRC).


I have decided to revert the change I have committed some time ago. I 
have run
the same test programs with cygwin and they do not print any sign. What you
are proposing sounds interesting but I do not think that the hassle to
implement that is worth, if the issue is not really required.  I do not have
the time to implement it.  Of course, you are welcome to provide an 
implementation
if you like.  I have done this patch for the sign behavior because I 
have assumed
that the way linux behave was the correct way.

Regards,
Juan M. Guerrero


Index: djgpp/src/libc/ansi/stdio/doprnt.c
===================================================================
RCS file: /cvs/djgpp/djgpp/src/libc/ansi/stdio/doprnt.c,v
retrieving revision 1.33
diff -U 5 -r1.33 doprnt.c
--- djgpp/src/libc/ansi/stdio/doprnt.c    5 Mar 2013 19:42:48 -0000    1.33
+++ djgpp/src/libc/ansi/stdio/doprnt.c    13 Mar 2013 19:57:27 -0000
@@ -388,11 +388,11 @@
        }
        else
        {
      ieee_value.ld = _ldouble;

-    if (ieee_value.ldt.sign && !IS_NAN(ieee_value) && 
!IS_PSEUDO_NUMBER(ieee_value))
+    if (ieee_value.ldt.sign)
      {
        neg_ldouble = true;
        if (IS_ZERO(ieee_value))
          softsign = '-';
      }

- Raw text -