box: Use isinf() and signbit() when isinff() is not available

Instead of using bytewise comparison, use isinf() and hope it works
correctly with single precision floats on the target platform;
additionally, since the negative return value for negative infinities is
a GNU extension, use signbit() to check if the number is a positive or
negative infinity.

src/graphene-box.c

@@ -436,18 +436,22 @@ graphene_box_is_empty (const graphene_box_t *box)
   return (isinff (vmin[0]) == 1 && isinff (vmin[1]) == 1 && isinff (vmin[2]) == 1) &&
          (isinff (vmax[0]) == -1 && isinff (vmax[1]) == -1 && isinff (vmax[2]) == -1);
 #else
-  graphene_simd4f_t neg_inf = graphene_simd4f_init (-INFINITY, -INFINITY, -INFINITY, 0.f);
-  graphene_simd4f_t pos_inf = graphene_simd4f_init (INFINITY, INFINITY, INFINITY, 0.f);
-
-  /* This is only every going to be valid for boxes that we have
-   * initialized ourselves, because we use the same values; the
-   * bitwise comparison will not hold for infinities generated by
-   * other operations
-   */
-  int min_cmp = memcmp (&box->min.value, &pos_inf, sizeof (graphene_simd4f_t));
-  int max_cmp = memcmp (&box->max.value, &neg_inf, sizeof (graphene_simd4f_t));
-
-  return min_cmp == 0 && max_cmp == 0;
+  float vmin[3], vmax[3];
+
+  graphene_simd4f_dup_3f (box->min.value, vim);
+  graphene_simd4f_dup_3f (box->max.value, vmax);
+
+  bool vmin_pos_inf =
+    (isinf (vmin[0]) && signbit (vmin[0]) == 0) &&
+    (isinf (vmin[1]) && signbit (vmin[1]) == 0) &&
+    (isinf (vmin[2]) && signbit (vmin[2]) == 0);
+
+  bool vmax_neg_inf =
+    (isinf (vmax[0]) && signbit (vmax[0]) < 0) &&
+    (isinf (vmax[1]) && signbit (vmax[1]) < 0) &&
+    (isinf (vmax[2]) && signbit (vmax[2]) < 0);
+
+  return vmin_pos_inf && vmax_neg_inf;
 #endif
 }
 
@@ -463,18 +467,22 @@ graphene_box_is_infinity (const graphene_box_t *box)
   return (isinff (vmin[0]) == -1 && isinff (vmin[1]) == -1 && isinff (vmin[2]) == -1) &&
          (isinff (vmax[0]) == 1 && isinff (vmax[1]) == 1 && isinff (vmax[2]) == 1);
 #else
-  graphene_simd4f_t neg_inf = graphene_simd4f_init (-INFINITY, -INFINITY, -INFINITY, 0.f);
-  graphene_simd4f_t pos_inf = graphene_simd4f_init (INFINITY, INFINITY, INFINITY, 0.f);
-
-  /* This is only every going to be valid for boxes that we have
-   * initialized ourselves, because we use the same values; the
-   * bitwise comparison will not hold for infinities generated by
-   * other operations
-   */
-  int min_cmp = memcmp (&box->min.value, &neg_inf, sizeof (graphene_simd4f_t));
-  int max_cmp = memcmp (&box->max.value, &pos_inf, sizeof (graphene_simd4f_t));
-
-  return min_cmp == 0 && max_cmp == 0;
+  float vmin[3], vmax[3];
+
+  graphene_simd4f_dup_3f (box->min.value, vim);
+  graphene_simd4f_dup_3f (box->max.value, vmax);
+
+  bool vmin_neg_inf =
+    (isinf (vmin[0]) && signbit (vmin[0]) < 0) &&
+    (isinf (vmin[1]) && signbit (vmin[1]) < 0) &&
+    (isinf (vmin[2]) && signbit (vmin[2]) < 0);
+
+  bool vmax_pos_inf =
+    (isinf (vmax[0]) && signbit (vmax[0]) == 0) &&
+    (isinf (vmax[1]) && signbit (vmax[1]) == 0) &&
+    (isinf (vmax[2]) && signbit (vmax[2]) == 0);
+
+  return vmin_neg_inf && vmax_pos_inf;
 #endif
 }