Re: [PATCH] fix printf regression with alt-form octal, default precision

[Rich Felker <dalias@libc.org>]

On Thu, Sep 15, 2016 at 09:14:56PM +0300, Dmitry V. Levin wrote:
> On Thu, Sep 15, 2016 at 12:37:57PM -0400, Rich Felker wrote:
> > On Thu, Aug 04, 2016 at 04:07:40AM +0300, Dmitry V. Levin wrote:
> > > commit v1.1.5-10-gb91cdbe2bc8b626aa04dc6e3e84345accf34e4b1 that fixed
> > > behavior of printf with alt-form octal, zero precision, zero value,
> > > at the same time broke alt-form octal with default precision,
> > > e. g. printf("%#09o", 1).
> > > ---
> > >  src/stdio/vfprintf.c | 9 ++++++++-
> > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
> > > index 2ecf769..ac2891c 100644
> > > --- a/src/stdio/vfprintf.c
> > > +++ b/src/stdio/vfprintf.c
> > > @@ -570,7 +570,14 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
> > >  			if (0) {
> > >  		case 'o':
> > >  			a = fmt_o(arg.i, z);
> > > -			if ((fl&ALT_FORM) && p<z-a+1) p=z-a+1;
> > > +			if (fl&ALT_FORM) {
> > > +				if (p >= 0 && p<z-a+1) {
> > > +					p=z-a+1;
> > > +				} else if (arg.i) {
> > > +					prefix+=5;
> > > +					pl=1;
> > > +				}
> > > +			}
> > >  			} if (0) {
> > >  		case 'd': case 'i':
> > >  			pl=1;
> > 
> > I think the attached simpler patch should work just as well. Adjusting
> > 'p' to implement '#' was probably a bad idea since it makes the later
> > code paths think an explicit precision was specified when it was not.
> > "Add a prefix of '0' when p is too short to have a leading '0'
> > already" seems like safer logic.
> > 
> > I'm also attaching some test cases I ran.
> > 
> > Rich
> > 
> > diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
> > index 2ecf769..e439a07 100644
> > --- a/src/stdio/vfprintf.c
> > +++ b/src/stdio/vfprintf.c
> > @@ -570,7 +570,7 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
> >  			if (0) {
> >  		case 'o':
> >  			a = fmt_o(arg.i, z);
> > -			if ((fl&ALT_FORM) && p<z-a+1) p=z-a+1;
> > +			if ((fl&ALT_FORM) && p<z-a+1) prefix+=5, pl=1;
> >  			} if (0) {
> >  		case 'd': case 'i':
> >  			pl=1;
> 
> Yes, this also works, thanks.

OK, I'm committing this version. Thanks!

Rich