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

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

SYNOPSIS
       #include 

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

       Link with -lm.

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

       logb():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 500 ||
           XOPENSOURCE && XOPENSOURCEEXTENDED || ISOC99SOURCE ||
           POSIXCSOURCE >= 200112L;
           or cc -std=c99
       logbf(), logbl():
           BSDSOURCE || SVIDSOURCE || XOPENSOURCE >= 600 ||
           ISOC99SOURCE || POSIXCSOURCE >= 200112L;
           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 inte‐
       ger constant FLTRADIX, defined in , indicates the radix  used
       for  the  system's  floating-point  representation.  If FLTRADIX 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
       -HUGEVAL, -HUGEVALF, or -HUGEVALL, respectively.

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

ERRORS
       See  matherror(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  (FEDIVBYZERO)  is
              raised.

       These functions do not set errno.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌─────────────────────────┬───────────────┬─────────┐
       │Interface                │ Attribute     │ Value   │
       ├─────────────────────────┼───────────────┼─────────┤
       │logb(), logbf(), logbl() │ Thread safety │ MT-Safe │
       └─────────────────────────┴───────────────┴─────────┘
CONFORMING TO
       C99, POSIX.1-2001.

SEE ALSO
       ilogb(3), log(3)

COLOPHON
       This page is part of release 3.53 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/.



                                  2010-09-20                           LOGB(3)