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Linux 2.6 - man page for log2 (linux section 3posix)

LOG2(P) 			    POSIX Programmer's Manual				  LOG2(P)

NAME
       log2, log2f, log2l - compute base 2 logarithm functions

SYNOPSIS
       #include <math.h>

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

DESCRIPTION
       These functions shall compute the base 2 logarithm of their argument x, log_2(x).

       An  application	wishing  to  check for error situations should set errno to zero and call
       feclearexcept(FE_ALL_EXCEPT) before calling these functions.  On return, if errno is  non-
       zero  or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,
       an error has occurred.

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

       If x is +-0, a pole error shall occur  and  log2(),  log2f(),  and  log2l()  shall  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 shall
       occur, and    either a NaN (if supported), or   an implementation-defined value	shall  be
       returned.

       If x is NaN, a NaN shall be returned.

       If x is 1, +0 shall be returned.

       If x is +Inf, x shall be returned.

ERRORS
       These functions shall fail if:

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

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is	non-zero,
       then the invalid floating-point exception shall be raised.

       Pole Error
	      The value of x is zero.

       If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be
       set to [ERANGE]. If the integer expression (math_errhandling  &	MATH_ERREXCEPT)  is  non-
       zero, then the divide-by-zero floating-point exception shall be raised.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On  error,  the	expressions  (math_errhandling	&  MATH_ERRNO)	and  (math_errhandling	&
       MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept()	,  fetestexcept()  ,   log()   ,   the	 Base	Definitions   volume   of
       IEEE Std 1003.1-2001,  Section  4.18, Treatment of Error Conditions for Mathematical Func-
       tions, <math.h>

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  LOG2(P)


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