class, _class, finite, isnan, or unordered Subroutines

Purpose

Determines classifications of floating-point numbers.

Libraries

IEEE Math Library (libm.a) or System V Math Library (libmsaa.a)

Syntax

#include <math.h>
#include <float.h>

int
class( x)
double x;

#include <math.h>
#include <float.h>

int
_class( x)
double x;

#include <math.h>
int finite(x)
double x;
#include <math.h>
int isnan(x)
double x;
#include <math.h>

int unordered(x, y)
double x, y;

Description

The class subroutine, _class subroutine, finite subroutine, isnan subroutine, and unordered subroutine determine the classification of their floating-point value. The unordered subroutine determines if a floating-point comparison involving x and y would generate the IEEE floating-point unordered condition (such as whether x or y is a NaN).

The class subroutine returns an integer that represents the classification of the floating-point x parameter. Since class is a reversed key word in C++. The class subroutine can not be invoked in a C++ program. The _class subroutine is an interface for C++ program using the class subroutine. The interface and the return value for class and _class subroutines are identical. The values returned by the class subroutine are defined in the float.h header file. The return values are the following:

Item Description
FP_PLUS_NORM Positive normalized, nonzero x
FP_MINUS_NORM Negative normalized, nonzero x
FP_PLUS_DENORM Positive denormalized, nonzero x
FP_MINUS_DENORM Negative denormalized, nonzero x
FP_PLUS_ZERO x = +0.0
FP_MINUS_ZERO x = -0.0
FP_PLUS_INF x = +INF
FP_MINUS_INF x = -INF
FP_NANS x = Signaling Not a Number (NaNS)
FP_NANQ x = Quiet Not a Number (NaNQ)

Since class is a reserved keyword in C++, the class subroutine cannot be invoked in a C++ program. The _class subroutine is an interface for the C++ program using the class subroutine. The interface and the return values for class and _class subroutines are identical.

The finite subroutine returns a nonzero value if the x parameter is a finite number; that is, if x is not +-, INF, NaNQ, or NaNS.

The isnan subroutine returns a nonzero value if the x parameter is an NaNS or a NaNQ. Otherwise, it returns 0.

The unordered subroutine returns a nonzero value if a floating-point comparison between x and y would be unordered. Otherwise, it returns 0.

Note: Compile any routine that uses subroutines from the libm.a library with the -lm flag. To compile the class.c file, for example, enter: 
cc class.c -lm

Parameters

Item Description
x Specifies some double-precision floating-point value.
y Specifies some double-precision floating-point value.

Error Codes

The finite, isnan, and unordered subroutines neither return errors nor set bits in the floating-point exception status, even if a parameter is an NaNS.