logb(3m) [sunos man page]

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

NAME

       logb, logbf, logbl - radix-independent exponent

SYNOPSIS

       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 logr |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 (see standards(5)), the exponent of x as if x were normalized is returned.

	 o  Otherwise, -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 5.10							    1 Nov 2003								  logb(3M)

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

NAME

       logb, logbf, logbl - radix-independent exponent

SYNOPSIS

       #include <math.h>

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

DESCRIPTION

       These functions shall 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.

       If x is subnormal it is treated as though it were normalized; thus for finite positive x:

	      1 <= x * FLT_RADIX**-logb(x) < FLT_RADIX

       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 exponent of x.

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

       If x is NaN, a NaN shall be returned.

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

ERRORS

       These functions shall fail if:

       Pole Error
	      The value of x is +-0.

       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() , ilogb() , scalb() , the Base Definitions volume of  IEEE Std 1003.1-2001,  Section  4.18,  Treatment	of
       Error Conditions for Mathematical Functions, <float.h>, <math.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- 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 original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								   LOGB(P)