HP-UX Reference (11i v2 04/09) - 3 Library Functions A-M (vol 6)

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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);

Itanium(R)-based System 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.

Itanium-based System 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 Itanium-based systems)

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.

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.

The macros

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

ERRORS

No errors are deﬁned.