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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  Func-
       tions, <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 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					  LOGB(P)
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