Re: printf POSIX compliance

[Rich Felker <dalias@aerifal.cx>]

On Fri, Jun 08, 2012 at 11:34:04AM +0100, Reuben Thomas wrote:
> I notice that the musl FAQ says "the fundamentally broken freadahead
> function in gnulib cannot be fixed by adding features to the C
> library". I found this question because a user complained about my use
> of gnulib in a package I maintain.
> 
> I contacted the gnulib maintainers, one of whom replied:
> 
> "IIRC, gnulib's freadahead use is caused by musl's printf not being
> posix compliant, causing gnulib to pull in its printf replacement,
> which doesn't work on musl."

The first failing test I found was invalid. It's a test for whether
printf supports printing non-finite long double values. gnulib is
constructing an illegal long double representation (which they call
"pseudo-denormal") that will never occur as a value and passing it to
printf:

|   { /* Pseudo-Denormal.  */
|     static union { unsigned int word[4]; long double value; } x =
|       { LDBL80_WORDS (0x0000, 0x83333333, 0x00000000) };
|     if (sprintf (buf, "%Lf", x.value) < 0
|         || !strisnan (buf, 0, strlen (buf)))
|       result |= 64;

This test should simply be removed; there is no reason printf should
handle invalid bit patterns that cannot occur as values.

The second failing test actually caught a slight bug in %ls with
precision modifiers. I've fixed it in musl git.

Still working on finding whether this long double issue is what's
causign the gnulib junk to get pulled in...

Rich