ilogb.3m (2010 09)

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ilogb(3M) ilogb(3M)

NAME

ilogb(), ilogbf(), ilogbl(), ilogbw(), ilogbq() - radix-independent exponent functions

SYNOPSIS

#include <math.h>

int ilogb(double x);

Integrity Server Only

int ilogbf(float x);

int ilogbl(long double x);

int ilogbw(extended x);

int ilogbq(quad x);

DESCRIPTION

The ilogb() function computes the exponent of the ﬂoating point value x. Formally, the return value is

the integral part of log base r of |x| as a signed integral value, for nonzero x, where r is the radix of the

machine’s ﬂoating-point arithmetic. The radix r is 2 on HP-UX systems.

If x is denormal it is treated as though it were normalized before the exponent is determined.

Note:

ilogb(x) is equivalent to (int)logb(x) for all values of x except NaN, ±INFINITY, and zero.

Integrity Servers Only

ilogbf() is a float version of ilogb(); it takes a float argument.

ilogbl() is a long double version of ilogb(); it takes a long double argument.

ilogbw() is an extended version of ilogb(); it takes an extended argument.

ilogbq() is equivalent to ilogbl() on HP-UX systems.

USAGE

To use these functions, compile either with the default

-Ae option or with the -Aa

and

-D_HPUX_SOURCE options.

To use (for Integrity servers)

ilogbw() or ilogbq(), compile also with the -fpwidetypes

option.

Make sure your program includes

<math.h>. Link in the math library by specifying -lm on the com-

piler or linker command line.

For more information, see the HP-UX ﬂoating-point guide for HP Integrity servers at the following site:

http://www.hp.com/go/fp

RETURN VALUE

If x is NaN,

ilogb() returns FP_ILOGBNAN.

If x is ±INFINITY,

ilogb() returns INT_MAX.

If x is zero,

ilogb() returns FP_ILOGB0.

Integrity Servers Only

If x is NaN, +-INFINITY, or zero, then the invalid ﬂoating-point exception is raised (as speciﬁed by C99

TC2)

The macros FP_ILOGBNAN and FP_ILOGB0 are deﬁned in <math.h>.

ERRORS

No errors are deﬁned.