HP-UX Reference (11i v1 05/09) - 3 Library Functions A-M (vol 6)

logb(3M) logb(3M)

NAME

logb( ) - radix-independent exponent

SYNOPSIS

#include <math.h>

double logb(double x);

DESCRIPTION

The logb() function computes the exponent of x. Formally, the return value is the integral part of log

base r of |x| as a signed ﬂoating point value, for nonzero x, where r is the radix of the machine’s ﬂoating-

point arithmetic.

The

logb() function is recommended by the IEEE-754 standard for ﬂoating-point arithmetic. The

ISO/ANSI C committee has approved the

logb() function for inclusion in the C9X draft standard.

To use this function, compile either with the default

-Ae option or with the -Aa and -D_HPUX_SOURCE

options. Make sure your program includes <

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

compiler or linker command line.

RETURN VALUE

Upon successful completion,

logb() returns the exponent of x.

If x is NaN, logb() returns NaN.

If x is ±INFINITY, logb() returns +INFINITY.

If x is zero,

logb() returns −HUGE_VAL and sets errno to [EDOM].

ERRORS

If logb() fails, errno is set to the following value.

[EDOM] x is zero.