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 positive.

log2f() is a float version of log2(); it takes a float argument and returns a float result. To use this function, compile either with the −Ae option or with the −Aa and −D_HPUX_SOURCE options. Otherwise, the compiler promotes the float argument to double, and the function returns incorrect results.

log2() and log2f() are not specified by any standard, but log2f() is named in accordance with the conventions specified in the "Future Library Directions" section of the ANSI C standard.

To use these functions, 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 negative, log2() returns NaN and sets errno to [EDOM].

ERRORS

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

[EDOM] x is negative.

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