From 44818a48273baa7dabfbb9370ac218ae8b0cf38e Mon Sep 17 00:00:00 2001
From: Neil Roberts <neil@linux.intel.com>
Date: Thu, 11 Feb 2010 14:20:48 +0000
Subject: [PATCH] cogl: Add a fallback for when the signbit macro is missing

The signbit macro is defined in C99 so it should be available but some
versions of GCC don't appear to define it by default. If it's not
available we can use a hack to test the bit directly.
---
 clutter/cogl/cogl/cogl-sub-texture.c |  2 +-
 clutter/cogl/cogl/cogl-texture-2d.c  |  2 +-
 clutter/cogl/cogl/cogl-util.h        | 27 ++++++++++++++++++++++++++-
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/clutter/cogl/cogl/cogl-sub-texture.c b/clutter/cogl/cogl/cogl-sub-texture.c
index bd23c857f..318282397 100644
--- a/clutter/cogl/cogl/cogl-sub-texture.c
+++ b/clutter/cogl/cogl/cogl-sub-texture.c
@@ -124,7 +124,7 @@ _cogl_sub_texture_unmap_coord (gfloat t,
   /* Convert the fractional part leaving the integer part in tact */
   frac_part = modff (t, &int_part);
 
-  if (signbit (frac_part))
+  if (cogl_util_float_signbit (frac_part))
     frac_part = ((1.0f + frac_part) * full_size -
                  sub_offset - sub_size) / sub_size;
   else
diff --git a/clutter/cogl/cogl/cogl-texture-2d.c b/clutter/cogl/cogl/cogl-texture-2d.c
index a86f84408..40f7b3f72 100644
--- a/clutter/cogl/cogl/cogl-texture-2d.c
+++ b/clutter/cogl/cogl/cogl-texture-2d.c
@@ -64,7 +64,7 @@ _cogl_texture_2d_wrap_coords (float t_1, float t_2,
   modff (t_1 < t_2 ? t_1 : t_2, &int_part);
   t_1 -= int_part;
   t_2 -= int_part;
-  if (signbit (int_part))
+  if (cogl_util_float_signbit (int_part))
     {
       *out_t_1 = 1.0f + t_1;
       *out_t_2 = 1.0f + t_2;
diff --git a/clutter/cogl/cogl/cogl-util.h b/clutter/cogl/cogl/cogl-util.h
index 589ddd35a..a6602a5f5 100644
--- a/clutter/cogl/cogl/cogl-util.h
+++ b/clutter/cogl/cogl/cogl-util.h
@@ -3,7 +3,7 @@
  *
  * An object oriented GL/GLES Abstraction/Utility Layer
  *
- * Copyright (C) 2007,2008,2009 Intel Corporation.
+ * Copyright (C) 2007,2008,2009,2010 Intel Corporation.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -24,7 +24,32 @@
 #ifndef __COGL_UTIL_H
 #define __COGL_UTIL_H
 
+#include <glib.h>
+#include <math.h>
+
 int
 cogl_util_next_p2 (int a);
 
+/* The signbit macro is defined by ISO C99 so it should be available,
+   however if it's not we can fallback to an evil hack */
+#ifdef signbit
+#define cogl_util_float_signbit(x) signbit(x)
+#else
+/* This trick was stolen from here:
+   http://lists.boost.org/Archives/boost/2006/08/108731.php
+
+   It xors the integer reinterpretations of -1.0f and 1.0f. In theory
+   they should only differ by the signbit so that gives a mask for the
+   sign which we can just test against the value */
+static inline gboolean
+cogl_util_float_signbit (float x)
+{
+  static const union { float f; guint32 i; } negative_one = { -1.0f };
+  static const union { float f; guint32 i; } positive_one = { +1.0f };
+  union { float f; guint32 i; } value = { x };
+
+  return !!((negative_one.i ^ positive_one.i) & value.i);
+}
+#endif
+
 #endif /* __COGL_UTIL_H */