logbl

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 ||
       _ISOC99_SOURCE; or cc -std=c99
       logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
       || _ISOC99_SOURCE; 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