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
If
log2()
fails,
errno
is set to the following value.
- [EDOM]
x
is less than zero.
