log2(3) [xfree86 man page]

LOG2(3) 						     Linux Programmer's Manual							   LOG2(3)

NAME

       log2, log2f, log2l - base-2 logarithmic function

SYNOPSIS

       #include <math.h>

       double log2(double x);
       float log2f(float x);
       long double log2l(long double x);

       Link with -lm.

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

       log2(), log2f(), log2l():
	   _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       These functions return the base 2 logarithm of x.

RETURN VALUE

       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).

ERRORS

       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).

VERSIONS

       These functions first appeared in glibc in version 2.1.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +-------------------------+---------------+---------+
       |Interface		 | Attribute	 | Value   |
       +-------------------------+---------------+---------+
       |log2(), log2f(), log2l() | Thread safety | MT-Safe |
       +-------------------------+---------------+---------+
CONFORMING TO

       C99, POSIX.1-2001, POSIX.1-2008.

       The variant returning double also conforms to SVr4, 4.3BSD.

SEE ALSO

       cbrt(3), clog2(3), log(3), log10(3), sqrt(3)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

								    2017-09-15								   LOG2(3)

log2(3M)						  Mathematical Library Functions						  log2(3M)

NAME

       log2, log2f, log2l - compute base 2 logarithm functions

SYNOPSIS

       c99 [ flag... ] file... -lm [ library... ]
       #include <math.h>

       double log2(double x);

       float log2f(float x);

       long double log2l(long double x);

DESCRIPTION

       These functions compute the base 2 logarithm of their argument x, log2(x).

RETURN VALUES

       Upon successful completion, these functions return the base 2 logarithm of x.

       If x is +-0, a pole error occurs and log2(), log2f(), and log2l() return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

       For finite values of x that are less than 0,  or if x is -Inf a domain error occurs and a NaN is returned.

       If x is NaN, a NaN is returned.

       If x is 1, +0 is returned.

       If x is +Inf, x is returned.

ERRORS

       These functions will fail if:

       Domain Error    The finite value of x is less than 0, or x is -Inf.

		       If  the	integer  expression  (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception is
		       raised.

       Pole Error      The value of x is 0.

		       If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception
		       is raised.

USAGE

       An  application	wanting  to  check  for  exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if
       fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception  has  been  raised.  An  application  should
       either examine the return value or check the floating point exception flags to detect exceptions.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       feclearexcept(3M), fetestexcept(3M), log(3M), math.h(3HEAD), attributes(5), standards(5)

SunOS 5.11							    12 Jul 2006 							  log2(3M)