Mathematical Library Functions                           logb(3M)



NAME
     logb, logbf, logbl - radix-independent exponent

SYNOPSIS
     c99 [ flag... ] file... -lm [ library... ]
     #include 

     double logb(double x);


     float logbf(float x);


     long double logbl(long double x);


     cc [ flag... ] file... -lm [ library... ]
     #include 

     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 FLTRADIX
     defined in the  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 normalized is returned.

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






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Mathematical Library Functions                           logb(3M)



     If x is ]0, a pole error occurs  and  logb(),  logbf(),  and
     logbl()   return   -HUGEVAL,  -HUGEVALF,  and  -HUGEVAL,
     respectively.


     If x is NaN, a NaN is returned.


     If x is ]Inf, ]Inf is returned.

ERORS
     These functions will fail if:

     Pole Error    The value of x is ]0.

                   If the integer expression (matherrhandling  &
                   MATHEREXCEPT)  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(FEALEXCEPT) before calling these functions.
     On  return,  if  fetestexcept(FEINVALID    FEDIVBYZERO  
     FEOVERFLOW    FEUNDERFLOW)  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.

ATRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:














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Mathematical Library Functions                           logb(3M)



     
           ATRIBUTE TYPE               ATRIBUTE 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), stan-
     dards(5)










































SunOS 5.11          Last change: 12 Jul 2006                    3