# logb(3p) [centos man page]

```LOGB(3P)						     POSIX Programmer's Manual							  LOGB(3P)

PROLOG
This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
logb, logbf, logbl - radix-independent exponent

SYNOPSIS
#include <math.h>

double logb(double x);
float logbf(float x);
long double logbl(long double x);

DESCRIPTION
These functions shall 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.

If x is subnormal it is treated as though it were normalized; thus for finite positive x:

An  application	wishing  to check for error situations should 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.

RETURN VALUE
Upon successful completion, these functions shall return the exponent of x.

If x is +-0, a pole error shall occur and logb(), logbf(), and logbl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

If x is NaN, a NaN shall be returned.

If x is +-Inf, +Inf shall be returned.

ERRORS
These functions shall fail if:

Pole Error
The value of x is +-0.

If  the	integer  expression  (math_errhandling	&  MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

The following sections are informative.

EXAMPLES
None.

APPLICATION USAGE
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of  each  other,  but	at
least one of them must be non-zero.

RATIONALE
None.

FUTURE DIRECTIONS
None.

feclearexcept(),  fetestexcept(),  ilogb(),  scalb(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error
Conditions for Mathematical Functions, <float.h>, <math.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group						       2003								  LOGB(3P)```

## Check Out this Related Man Page

```SCALB(3P)						     POSIX Programmer's Manual							 SCALB(3P)

PROLOG
This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

SYNOPSIS
#include <math.h>

double scalb(double x, double n);

DESCRIPTION
The scalb() function shall compute x*r**n, where r is the radix of the machine's floating-point arithmetic. When r is 2, scalb()  shall	be
equivalent to ldexp(). The value of r is FLT_RADIX which is defined in <float.h>.

An  application	wishing  to check for error situations should 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.

RETURN VALUE
Upon successful completion, the scalb() function shall return x*r**n.

If x or n is NaN, a NaN shall be returned.

If n is zero, x shall be returned.

If x is +-Inf and n is not -Inf, x shall be returned.

If x is +-0 and n is not +Inf, x shall be returned.

If  x  is  +-0  and  n  is  +Inf,  a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be
returned.

If x is +-Inf and n is -Inf, a domain error shall occur, and either a NaN (if supported),  or  an  implementation-defined  value  shall	be
returned.

If the result would cause an overflow, a range error shall occur and +-HUGE_VAL (according to the sign of x) shall be returned.

If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

If the correct value would cause underflow, and is not representable, a range error may occur, and 0.0 shall be returned.

ERRORS
The scalb() function shall fail if:

Domain Error
If x is zero and n is +Inf, or x is Inf and n is -Inf.

If  the	integer  expression  (math_errhandling	&  MATH_ERRNO)	is  non-zero, then errno shall be set to [EDOM]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

Range Error
The result would overflow.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set  to  [ERANGE].  If  the  integer	expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

The scalb() function may fail if:

Range Error
The result underflows.

If  the	integer  expression  (math_errhandling	&  MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

The following sections are informative.

EXAMPLES
None.

APPLICATION USAGE
Applications should use either scalbln(), scalblnf(), or scalblnl() in preference to this function.

IEEE Std 1003.1-2001 only defines the behavior for the scalb() function when the n argument is an integer, a NaN, or Inf. The  behavior	of
other values for the n argument is unspecified.

On  error,  the	expressions  (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.

RATIONALE
None.

FUTURE DIRECTIONS
None.