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); |
Link with −lm.
These functions extract the exponent of x and return it as a
floating-point value. If FLT_RADIX is two, logb(x) is equal to
floor(log2(x)),
except it's probably faster.
If x is
de-normalized, logb() returns
the exponent x would
have if it were normalized.
If x is zero,
−HUGE_VAL (resp. −HUGE_VALF, −HUGE_VALL) is
returned, and a pole error occurs. If x is infinite, plus infinity is
returned. If x is
NaN, NaN is returned.
In order to check for errors, set errno to zero and call feclearexcept(FE_ALL_EXCEPT)
before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO |
FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error
has occurred.
If an error occurs and (math_errhandling & MATH_ERRNO) is non-zero, then errno is set to ERANGE. If an error occurs and (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised.
A pole error occurs when x is zero.
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