Tribblix: manual page: logb.3m

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 log(r) |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:

o For SUSv3-conforming applications compiled with the c99
compiler driver (see standards(7)), the exponent of x as
if x were normalized is returned.

o Otherwise, if compiled with the cc compiler driver, -1022,
-126, and -16382 are returned for logb(), logbf(), and
logbl(), respectively.

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
floating-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
feclearexcept(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