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.
DESCRIPTION
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.
ERRORS
In order to check for errors, set errno to zero and call feclearex‐
cept(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.
HISTORY
The logb() function occurs in 4.3BSD.
CONFORMING TO
C99
SEE ALSOlog(3), ilogb(3)
2004-10-31 LOGB(3)