RE: crashing bug : found... destroyed

["Harold Hunt" <huntharo at msu dot edu>]

Alan,

What do you think?  It sounds logical to me... do you want to commit it if
it seems straight to you?

Harold

> -----Original Message-----
> From: cygwin-xfree-owner@sources.redhat.com
> [mailto:cygwin-xfree-owner@sources.redhat.com]On Behalf Of Brian Michael
> Genisio
> Sent: Tuesday, July 31, 2001 2:14 PM
> To: cygwin-xfree@sources.redhat.com
> Subject: crashing bug : found... destroyed
>
>
> I wanted to report a bug I found in the XWin server. ( It pops up in
>  the VFB and probably Xnest as well.)  It has to do with the
> drawing of poly
> lines. Unfortunately, I do not have a program I can give you to
> recreate the
> bug, but take a look, and hopefully add the fix the the XFree source.
>
> The problem is in the  mi/miwideline.c file.  It makes use of the
> math function
> hypot ( hypotonuse ... sqrt(a*a + b*b) ) from math.h.  Because of
> the way the
> defines are set up in the beginning, this file never gets an appropriate
> prototype for `double hypot(double, double) `.
>
> Since it had no proper prototype, I am assuming it was storing
> the value as a
> float or int, instead of a double and the value in the line
>
> L = hypot ((double) dx, (double) dy);
>
> (inside the miWideSegment function) was being stored badly,
> causing unexpected
> results... sometimes a crash due to data overwrites (which I was
> running into).
>
> This has probably been run into before, since in the beginning of
> the file, we
> see this code :
>
> #ifdef _XOPEN_SOURCE
> #include <math.h>
> #else
> #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> #include <math.h>
> #undef _XOPEN_SOURCE
> #endif
>
> I looked at the math.h file on my solaris box, and I see that hypot is
> prototyped if _XOPEN_SOURCE is defined.  Soo.... it looks like it
> was an issue
> for solaris.  Unfortunately, math.h in cygwin does not use the define
> _XOPEN_SOURCE to determine when to use hypot.
>
> Instead, it prototypes hypot ONLY when __STRICT_ANSI__ is NOT
> defined.  Well,
> in the build of this file, STRICT_ANSI must be getting defined,
> since I have
> determined that hypot is not being prototyped.  I determined this
> by compiling
> miwideline.c with all of the XFree flags, and included the -E
> option, which
> preprocesses the file, but does not compile it.  This output
> proved that hypot
> was not being prototyped.
>
>
>
>
>
> THE FIX :
> I simply undefine __STRICT_ANSI__ before the math.h include, and
> redefine it
> after :
>
>
>
> #if defined(__STRICT_ANSI__) && defined(__CYGWIN__)
> #undef __STRICT_ANSI__ /* undefine to insure hypot */
>
> #ifdef _XOPEN_SOURCE
> #include <math.h>
> #else
> #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> #include <math.h>
> #undef _XOPEN_SOURCE
> #endif
>
> #define __STRICT_ANSI__
> #else /*#if defined(__STRICT_ANSI__) && defined(__CYGWIN__)*/
>
> #ifdef _XOPEN_SOURCE
> #include <math.h>
> #else
> #define _XOPEN_SOURCE   /* to get prototype for hypot on some systems */
> #include <math.h>
>
> #undef _XOPEN_SOURCE
> #endif
>
> #endif /*#if defined(__STRICT_ANSI__) && defined(__CYGWIN__)*/
>
>
>
>
> By putting this at the beginning of the file, instead of the old
> version (noted
> above), the bug is worked around... but we may run into it with
> other files.
> Either way, I hope this fix can be incorporated into the XFree code.
>
> Thanks,
> Brian
>
>
>
>
> --
> ---------------------------
> Brian Genisio
> genisiob@pilot.msu.edu
>
>
>
>
>