logb, logbf, logbl - get exponent of a floating-point value
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
These functions extract the exponent from the internal floating-point
representation of x and return it as a floating-point value.
The integer 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 similar to
floor(log2(fabs(x))), except
that the latter may give an incorrect integer due to intermediate
rounding.
If x is subnormal, logb() returns the
exponent x would have if it were normalized.
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.