printf %05f on infinity

[Jeff Johnston]

Ok, but leave out the URL reference in the comment.

-- Jeff J.

Eric Blake wrote:
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> C99 basically requires the intuitive relation that if printf can generate
> something using a single % specifier, scanf can restore the same value
> (well, with the caveat that scanf can use a canonical NaN instead of
> supporting all 2^53 of them, and within the limits of rounding if the
> printf precision was too small).  Or, more directly,
>
> "C99+TC1+TC2: 7.19.6.1 The fprintf function
> Paragraph 6, discussion on the '0' flag:  ... leading zeros ...
> are used to pad to the field width rather than performing space
> padding, except when converting an infinity or NaN."
> http://www.opengroup.org/austin/mailarchives/ag/msg10445.html
>
> So printf("%05f",1./0) should result in "  inf", not "00inf".  OK to apply?
>
> 2007-04-12  Eric Blake  <ebb9@byu.net>
>
> 	* libc/stdio/vfprintf.c (_VFPRINTF_F): Don't zero pad on infinity
> 	or NaN with %05f.
>
> - --
> Don't work too hard, make some time for fun as well!
>
> Eric Blake             ebb9@byu.net
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>   
> ------------------------------------------------------------------------
>
> Index: libc/stdio/vfprintf.c
> ===================================================================
> RCS file: /cvs/src/src/newlib/libc/stdio/vfprintf.c,v
> retrieving revision 1.49
> diff -u -p -r1.49 vfprintf.c
> --- libc/stdio/vfprintf.c	13 Apr 2007 01:57:33 -0000	1.49
> +++ libc/stdio/vfprintf.c	13 Apr 2007 02:18:02 -0000
> @@ -872,7 +872,14 @@ reswitch:	switch (ch) {
>  				_fpvalue = GET_ARG (N, ap, double);
>  			}
>  
> -			/* do this before tricky precision changes */
> +			/* do this before tricky precision changes
> +
> +			   If the output is infinite or NaN, leading
> +			   zeros are not permitted.  Otherwise, scanf
> +			   could not read what print wrote.
> +
> +			   http://www.opengroup.org/austin/mailarchives/ag/msg10445.html
> +		       */
>  			if (isinf (_fpvalue)) {
>  				if (_fpvalue < 0)
>  					sign = '-';
> @@ -881,6 +888,7 @@ reswitch:	switch (ch) {
>  				else
>  					cp = "inf";
>  				size = 3;
> +				flags &= ~ZEROPAD;
>  				break;
>  			}
>  			if (isnan (_fpvalue)) {
> @@ -889,11 +897,12 @@ reswitch:	switch (ch) {
>  				else
>  					cp = "nan";
>  				size = 3;
> +				flags &= ~ZEROPAD;
>  				break;
>  			}
>  
>  #else /* !_NO_LONGDBL */
> -			
> +
>  			if (flags & LONGDBL) {
>  				_fpvalue = GET_ARG (N, ap, _LONG_DOUBLE);
>  			} else {
> @@ -910,6 +919,7 @@ reswitch:	switch (ch) {
>  				else
>  					cp = "inf";
>  				size = 3;
> +				flags &= ~ZEROPAD;
>  				break;
>  			}
>  			if (tmp == 1) {
> @@ -918,6 +928,7 @@ reswitch:	switch (ch) {
>  				else
>  					cp = "nan";
>  				size = 3;
> +				flags &= ~ZEROPAD;
>  				break;
>  			}
>  #endif /* !_NO_LONGDBL */
>