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CC, Language topics, Predefined Macros, Floating Point Macros
 *Conan The Librarian 

  HP C automatically defines the following predefined macros
  pertaining to the format of floating-point variables.  You can use
  them to identify the format with which you are compiling your
  program:

  __D_FLOAT
  __G_FLOAT
  __IEEE_FLOAT
  _IEEE_FP
  __X_FLOAT
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