_fpclass, _fpclassl

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Header File

float.h

Prototype

int _fpclass(double d);
int _fpclassl(long double ld);

Description

Returns an integer value representing the type (class) of an IEEE real for doubles. This value contains information on the floating-point class of the argument.

_fpclassl is the long double version; it takes a long double argument and returns the type (class) of an IEEE real for long doubles.

Return Value

Returns an integer value that indicates the floating-point class of its argument. The possible values, which are listed in the table below, are defined in FLOAT.H.

_FPCLASS_UNSUP	Unsupported IEEE format
_FPCLASS_SNAN	Signaling NaN
_FPCLASS_QNAN	Quiet NaN
_FPCLASS_NINF	Negative infinity
_FPCLASS_NN	Negative normalized non-zero
_FPCLASS_ND	Negative denormal
_FPCLASS_NZ	Negative zero (-0.0)
_FPCLASS_PZ	Positive zero (+0.0)
_FPCLASS_PD	Positive denormal
_FPCLASS_PN	Positive normalized non-zero
_FPCLASS_PINF	Positive infinity

Portability

	POSIX	ANSI C	ANSI C++	Win32	Win64	OS X
_fpclass				+
_fpclassl				+

Example

#include <float.h>
#include <stdio.h>

/* Compare a and b */
int compare(double a, double b) {
	/* Only if both are finite. */
	if (_finite(a) && _finite(b)) {
		if (a < b)
			return -1;
		else if (a > b)
			return 1;
		else
			return 0;
	}
	else {
		/* For infinite values check the class of the numbers */
		int class_a = _fpclass(a);
		int class_b = _fpclass(b);

		/* No check the infinities and compare them */
		if (class_a == _FPCLASS_NINF) {
			if (class_b ==  _FPCLASS_NINF)
				return 0;
			else
				return -1;
		}
		else if (class_a == _FPCLASS_PINF) {
			if (class_b == _FPCLASS_PINF)
				return 0;
			else
				return 1;
		}
	}

	/* Cannot find a relationship! */
	return -1;
}