Originální popis anglicky:
logb, logbf, logbl - get exponent of a floating point value
Návod, kniha: Linux Programmer's Manual
#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.
The
logb function occurs in BSD 4.3.
ISO C99
log(3),
ilogb(3)
