logb(3M) Mathematical Library Functions logb(3M)NAME
logb, logbf, logbl - radix-independent exponent
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);
cc [ flag... ] file... -lm [ library... ]
#include <math.h>
double logb(double x);
float logbf(float x);
long double logbl(long double x);
DESCRIPTION
These functions compute the exponent of x, which is the integral part
of logr |x|, as a signed floating point value, for non-zero x, where r
is the radix of the machine's floating-point arithmetic, which is the
value of FLT_RADIX defined in the <float.h> header.
RETURN VALUES
Upon successful completion, these functions return the exponent of x.
If x is subnormal:
· For SUSv3-conforming applications compiled with the c99 compiler
driver (see standards(5)), the exponent of x as if x were normal‐
ized is returned.
· Otherwise, if compiled with the cc compiler driver, −1022, −126,
and −16382 are returned for logb(), logbf(), and logbl(), respec‐
tively.
If x is ±0, a pole error occurs and logb(), logbf(), and logbl() return
−HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively.
If x is NaN, a NaN is returned.
If x is ±Inf, +Inf is returned.
ERRORS
These functions will fail if:
Pole Error The value of x is ±0.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the divide-by-zero float‐
ing-point exception is raised.
The logb() function sets errno to EDOM if the value of
x is 0.
USAGE
An application wanting to check for exceptions should call feclearex‐
cept(FE_ALL_EXCEPT) before calling these functions. On return, if
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an exception has been raised. An application should either
examine the return value or check the floating point exception flags to
detect exceptions.
An application can also set errno to 0 before calling logb(). On
return, if errno is non-zero, an error has occurred. The logbf() and
logbl() functions do not set errno.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOfeclearexcept(3M), fetestexcept(3M), ilogb(3M), math.h(3HEAD), math‐
err(3M), scalb(3M), attributes(5), standards(5)SunOS 5.10 12 Jul 2006 logb(3M)
