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

log2(3M) log2(3M)

NAME

log2(), log2f() - logarithm base two functions

SYNOPSIS

#include <math.h>

double log2(double x);

float log2f(float x);

DESCRIPTION

log2() returns the logarithm base two of x. The value of x must be greater than zero.

The ISO/ANSI C committee has approved the

log2() function for inclusion in the C9X draft standard.

log2f() is a float version of log2()

; it takes a float argument and returns a float result.

log2f() is not speciﬁed by any standard, but it is named in accordance with the conventions speciﬁed in

the "Future Library Directions" section of the ANSI C standard.

To use these functions, 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

If x is +INFINITY, log2() returns +INFINITY.

If x is zero,

log2() returns −HUGE_VAL.

If x is NaN, log2() returns NaN.

If x is less than zero, log2() returns NaN and sets errno to [EDOM].

ERRORS

log2() fails, errno is set to the following value.

[EDOM] x is less than zero.