__floating_type

   /* 1 if 'type' is a floating type, 0 if 'type' is an integer type.
     Allows for _Bool.  Expands to an integer constant expression.  */
  #define __floating_type(type) (((type) 0.25) && ((type) 0.25 - 1))

以下を考えれば簡単

(int)0.25 == 0
(_Bool)0.25 == 1
(float)0.25 == 0.25f
(double)0.25 == 0.25