[Mesa-dev] Mesa (master): Use signbit() in IS_NEGATIVE and DIFFERENT_SIGNS

[Patrick Baggett]

Concurrency::precise_math::signbit(), and only as of VS 2012 runtimes. This
is an awfully high bar for such a simple function.



On Mon, Sep 24, 2012 at 1:43 PM, Matt Turner <mattst88 at gmail.com> wrote:

> On Mon, Sep 24, 2012 at 11:02 AM, Brian Paul <brianp at vmware.com> wrote:
> > On 09/24/2012 10:49 AM, Matt Turner wrote:
> >>
> >> Module: Mesa
> >> Branch: master
> >> Commit: 0f3ba405eada72e1ab4371948315b28608903927
> >> URL:
> >>
> http://cgit.freedesktop.org/mesa/mesa/commit/?id=0f3ba405eada72e1ab4371948315b28608903927
> >>
> >> Author: Matt Turner<mattst88 at gmail.com>
> >> Date:   Fri Sep 14 16:04:40 2012 -0700
> >>
> >> Use signbit() in IS_NEGATIVE and DIFFERENT_SIGNS
> >>
> >> signbit() appears to be available everywhere (even MSVC according to
> >> MSDN), so let's use it instead of open-coding some messy and confusing
> >> bit twiddling macros.
> >>
> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54805
> >> Reviewed-by: Paul Berry<stereotype441 at gmail.com>
> >> Suggested-by: Ian Romanick<ian.d.romanick at intel.com>
> >>
> >> ---
> >>
> >>   configure.ac           |    7 +++++++
> >>   src/mesa/main/macros.h |   21 ++-------------------
> >>   2 files changed, 9 insertions(+), 19 deletions(-)
> >>
> >> diff --git a/configure.ac b/configure.ac
> >> index 4193496..cb65467 100644
> >> --- a/configure.ac
> >> +++ b/configure.ac
> >> @@ -499,6 +499,13 @@ AC_SUBST([DLOPEN_LIBS])
> >>   dnl See if posix_memalign is available
> >>   AC_CHECK_FUNC([posix_memalign], [DEFINES="$DEFINES
> >> -DHAVE_POSIX_MEMALIGN"])
> >>
> >> +dnl signbit() is a macro in glibc's math.h, so AC_CHECK_FUNC fails. To
> >> handle
> >> +dnl this, use AC_CHECK_DECLS and fallback to AC_CHECK_FUNC in case it
> >> fails.
> >> +AC_CHECK_DECLS([signbit],[],
> >> +               AC_CHECK_FUNC([signbit],[],
> >> +                             AC_MSG_ERROR([could not find signbit()])),
> >> +               [#include<math.h>])
> >> +
> >>   dnl SELinux awareness.
> >>   AC_ARG_ENABLE([selinux],
> >>       [AS_HELP_STRING([--enable-selinux],
> >> diff --git a/src/mesa/main/macros.h b/src/mesa/main/macros.h
> >> index 04d59d7..7b7fd1b 100644
> >> --- a/src/mesa/main/macros.h
> >> +++ b/src/mesa/main/macros.h
> >> @@ -693,31 +693,14 @@ NORMALIZE_3FV(GLfloat v[3])
> >>   static inline GLboolean
> >>   IS_NEGATIVE(float x)
> >>   {
> >> -#if defined(USE_IEEE)
> >> -   fi_type fi;
> >> -   fi.f = x;
> >> -   return fi.i<  0;
> >> -#else
> >> -   return x<  0.0F;
> >> -#endif
> >> +   return signbit(x) != 0;
> >>   }
> >>
> >> -
> >>   /** Test two floats have opposite signs */
> >>   static inline GLboolean
> >>   DIFFERENT_SIGNS(GLfloat x, GLfloat y)
> >>   {
> >> -#if defined(USE_IEEE)
> >> -   fi_type xfi, yfi;
> >> -   xfi.f = x;
> >> -   yfi.f = y;
> >> -   return !!((xfi.i ^ yfi.i)&  (1u<<  31));
> >> -#else
> >> -   /* Could just use (x*y<0) except for the flatshading requirements.
> >> -    * Maybe there's a better way?
> >> -    */
> >> -   return ((x) * (y)<= 0.0F&&  (x) - (y) != 0.0F);
> >> -#endif
> >> +   return signbit(x) != signbit(y);
> >>   }
> >>
> >>
> >
> > Looks like we don't have signbit() on Windows.  We build with scons
> there so
> > the autoconf check isn't applicable.  I'll post a patch in a bit.
> >
> > -Brian
>
> MSDN claims that Windows does have signbit():
> http://msdn.microsoft.com/en-us/library/hh308342.aspx
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