[Chicken-hackers] [PATCH] Fix #566 and simplify/improve flonum printing code

[Peter Bex]

Hi all,

In order to fix #566, I decided it's much easier to rip out the
HAVE_GCVT definition in Cygwin.  After testing on several platforms,
it turns out that gcvt() is really not required, and it's deprecated
by POSIX as well.  So we should probably stop using it anyway; this
also simplifies testing as it doesn't needlessly use different library
functions on different platforms.

I tried to figure out why HAVE_GCVT was introduced in the first place,
but it goes all the way back to the very first commit in the NonGNU CVS
even.  Felix mentioned that he seemed to recall that it had something
to do with making behaviour of the various Windows builds consistent
among eachother.

However, I've tested all three Windows builds, and they all behave
equally well (or better) with s[n]printf() instead of gcvt().  We no
longer have a MSVC build, so the original problem probably was there,
or it was in an older version of Cygwin/MingW which has been fixed in
the meanwhile (it's been over 10 years, so a thing or two will have
changed there, as well!).  If we ever regain a MSVC build, we can
look at restoring this code, but in the meanwhile I prefer the
simplicity of this solution.  I was even able to get rid of the
MINGW hack just below the changed code!

I've also taken the opportunity to convert sprintf into a checked
snprintf.  I'm not 100% sure but I don't think this requires a CVE
since you can't easily (at all?) cause over 4096 flonum digits to
get printed, and flonum-print-precision is rarely, if ever
user-controlled.  Feel free to request a CVE if you disagree.

Cheers,
Peter
-- 
http://www.more-magic.net

0001-Remove-HAVE_GCVT-check-and-definition.-Use-snprintf-.patch
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