mirrors/cosmopolitan
1
0
Fork 0
mirror of https://github.com/jart/cosmopolitan.git synced 2025-08-04 08:50:27 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

Fix issues 774, 782 and 789 (printf precision bugs) (#790)

Browse source 
The C standard states that, within the context of a printf-family
function, when specifying the precision of a conversion specification:

> A negative precision argument is taken as if the precision were
> omitted.
- Quoth the C Standard, 7.23.6.1. The fprintf function

Cosmopolitan instead treated negative precision arguments as
though they had a value of 0, which was non-conforming. This
change fixes that. Another issue we found relates to:

> For o conversion, it increases the precision, if and only if
> necessary, to force the first digit of the result to be a zero (if
> the value and precision are both 0, a single 0 is printed).
- Quoth the C standard, 7.23.6.1.6. The fprintf function

When printing numbers in their alternative form, with a precision and
with a conversion specifier of o (octal), Cosmopolitan wasn't following
the standard in two ways:

1. When printing a value with a precision that results in 0-padding,
   cosmopolitan would still add an extra 0 even though this should be
   done "if and only if necessary"
2. When printing a value of 0 with a precision of 0, nothing is
   printed, even though the standard specifically states that a single
   0 is printed in this case

This change fixes those issues too. Furthermore, regression tests have
been introduced to ensure Cosmopolitan continues to be conformant
going forward.

Fixes #774 
Fixes #782 
Fixes #789
This commit is contained in:
Gabriel Ravier 2023-03-29 10:11:48 +02:00 • committed by GitHub
parent 2f4335e081
commit 7f925e6be9
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
3 changed files with 33 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

4
libc/fmt/fmt.c
View file

@ -16,10 +16,11 @@
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/fmt/fmt.h"
#include "libc/assert.h"
#include "libc/errno.h"
#include "libc/fmt/conv.h"
#include "libc/fmt/fmt.h"
#include "libc/fmt/fmt.internal.h"
#include "libc/fmt/internal.h"
#include "libc/fmt/itoa.h"
@ -255,6 +256,7 @@ _Hide int __fmt(void *fn, void *arg, const char *format, va_list va) {
}
if (prec < 0) {
prec = 0;
flags &= ~FLAGS_PRECISION;
}
// evaluate length field