ultrix man page for fp_class

fp_class(3)						     Library Functions Manual						       fp_class(3)

Name
       fp_class - classes of IEEE floating-point values

Syntax
       #include <fp_class.h>

       int fp_class_d(double x);
       int fp_class_f(float x);

Description
       These routines are used to determine the class of IEEE floating-point values.  They return one of the constants in the file and never cause
       an exception, even for signaling NaNs.  These routines are to implement the recommended function class(x)  in  the  appendix  of  the  IEEE
       754-1985 standard for binary floating-point arithmetic.	The constants in refer to the following classes of values:

       Constant       Class
       FP_SNAN	      Signaling NaN (Not-a-Number)
       FP_QNAN	      Quiet NaN (Not-a-Number)
       FP_POS_INF     +oo (positive infinity)
       FP_NEG_INF     -oo (negative infinity)
       FP_POS_NORM    positive normalized nonzero
       FP_NEG_NORM    negative normalized nonzero
       FP_POS_DENORM  positive denormalized
       FP_NEG_DENORM  negative denormalized
       FP_POS_ZERO    +0.0 (positive zero)
       FP_NEG_ZERO    -0.0 (negative zero)

Also See
       ANSI/IEEE Std 754-1985, IEEE Standard for Binary Floating-Point Arithmetic

								       RISC							       fp_class(3)