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

[Brian Paul]

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