# logbf(3m) [sunos man page]

```logb(3M)						  Mathematical Library Functions						  logb(3M)

NAME
logb, logbf, logbl - radix-independent exponent

SYNOPSIS
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:

o  For SUSv3-conforming applications (see standards(5)), the exponent of x as if x were normalized is returned.

o  Otherwise, -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
See attributes(5) for descriptions of the following attributes:

+-----------------------------+-----------------------------+
|      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
+-----------------------------+-----------------------------+
|Interface Stability	     |Standard			   |
+-----------------------------+-----------------------------+
|MT-Level		     |MT-Safe			   |
+-----------------------------+-----------------------------+

feclearexcept(3M), fetestexcept(3M), ilogb(3M), math.h(3HEAD), matherr(3M), scalb(3M), attributes(5), standards(5)

SunOS 5.10							    1 Nov 2003								  logb(3M)```

## Check Out this Related Man Page

```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);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

logb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or cc -std=c99
logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION
These  functions  extract  the  exponent from the internal floating-point representation of x and return it as a floating-point value.  The
integer constant FLT_RADIX, defined in <float.h>, indicates the radix used for the system's floating-point representation.  If FLT_RADIX is
2, logb(x) is equal to floor(log2(x)), except that it is probably faster.

If x is subnormal, logb() returns the exponent x would have if it were normalized.

RETURN VALUE
On success, these functions return the exponent of x.

If x is a NaN, a NaN is returned.

If x is zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

If x is negative infinity or positive infinity, then positive infinity is returned.

ERRORS
See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Pole error: x is 0
A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

These functions do not set errno.

CONFORMING TO
C99, POSIX.1-2001.