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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 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99
       logbf(), logbl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 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 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 3.53 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)