logb(3m) [opensolaris man page]

logb(3M)						  Mathematical Library Functions						  logb(3M)

NAME

       logb, logbf, logbl - radix-independent exponent

SYNOPSIS

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

       double logb(double x);

       float logbf(float x);

       long double logbl(long double x);

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

       double logb(double x);

       float logbf(float x);

       long double logbl(long double x);

DESCRIPTION

       These  functions  compute  the  exponent  of x, which is the integral part of log(r) |x|, as a signed floating point value, for non-zero x,
       where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the <float.h> header.

RETURN VALUES

       Upon successful completion, these functions return the exponent of x.

       If x is subnormal:

	   o	  For SUSv3-conforming applications compiled with the c99 compiler driver (see standards(5)), the exponent of x as if x were  nor-
		  malized is returned.

	   o	  Otherwise,  if  compiled  with  the  cc  compiler driver, -1022, -126, and -16382 are returned for logb(), logbf(), and logbl(),
		  respectively.

       If x is +-0, a pole error occurs and logb(), logbf(), and logbl() return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

       If x is NaN, a NaN is returned.

       If x is +-Inf, +Inf is returned.

ERRORS

       These functions will fail if:

       Pole Error    The value of x is +-0.

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

		     The logb() function sets errno to EDOM if the value of x is 0.

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.

       An  application	can  also  set	errno  to 0 before calling logb(). On return, if errno is non-zero, an error has occurred. The logbf() and
       logbl() functions do not set errno.

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), ilogb(3M), math.h(3HEAD), matherr(3M), scalb(3M), attributes(5), standards(5)

SunOS 5.11							    12 Jul 2006 							  logb(3M)

Check Out this Related Man Page

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

NAME

       logb, logbf, logbl - get exponent of a floating-point value

SYNOPSIS

       #include <math.h>

       double logb(double x);
       float logbf(float x);
       long double logbl(long double x);

       Link with -lm.

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

       logb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
       logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION

       These  functions  extract  the  exponent from the internal floating-point representation of x and return it as a floating-point value.  The
       integer constant FLT_RADIX, defined in <float.h>, indicates the radix used for the system's floating-point representation.  If FLT_RADIX is
       2, logb(x) is equal to floor(log2(x)), except that it is probably faster.

       If x is subnormal, logb() returns the exponent x would have if it were normalized.

RETURN VALUE

       On success, these functions return the exponent of x.

       If x is a NaN, a NaN is returned.

       If x is zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

       If x is negative infinity or positive infinity, then positive infinity is returned.

ERRORS

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

       The following errors can occur:

       Pole error: x is 0
	      A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

       These functions do not set errno.

CONFORMING TO

       C99, POSIX.1-2001.

SEE ALSO

       ilogb(3), log(3)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

								    2008-08-05								   LOGB(3)

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logb(3m) [opensolaris man page]

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