Base-2 logarithmic function

#include <math.h>double log2(doublex);float log2f(floatx);long double log2l(long doublex);

Link with *-lm*.

Feature Test Macro Requirements for glibc (see **feature_test_macros**(7)):

**log2**(), **log2f**(), **log2l**():

_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

The **log2**() function returns the base 2 logarithm of *x*.

On success, these functions return the base 2 logarithm of *x*.

For special cases, including where *x* is 0, 1, negative, infinity, or NaN, see **log**(3).

See **math_error**(7) for information on how to determine whether an error has occurred when calling these functions.

For a discussion of the errors that can occur for these functions, see **log**(3).

These functions first appeared in glibc in version 2.1.

C99, POSIX.1-2001. The variant returning *double* also conforms to SVr4, 4.3BSD.

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