# 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 exponentSYNOPSIS

#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: 1 <= x * FLT_RADIX**-logb(x) < FLT_RADIX 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, and-HUGE_VALF, respectively. If x is NaN, a NaN shall be returned. If x is +-Inf, +Inf shall be returned.-HUGE_VALLERRORS

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.SEE ALSO

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>COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogyPortable 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

scalb - load exponent of a radix-independent floating-point numberSYNOPSIS

#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, 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.-InfERRORS

The scalb() function shall fail if: Domain Error If x is zero and n is +Inf, or x is Inf and n isIf 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.-Inf.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.SEE ALSO

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

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogyPortable 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 SCALB(3P)