# scalbln - Man Page

compute exponent using FLT_RADIX

## Prolog

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

## Synopsis

#include <math.h> double scalbln(doublex, longn); float scalblnf(floatx, longn); long double scalblnl(long doublex, longn); double scalbn(doublex, intn); float scalbnf(floatx, intn); long double scalbnl(long doublex, intn);

## Description

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

These functions shall compute *x* * FLT_RADIX^{n} efficiently, not normally by computing FLT_RADIX^{n} explicitly.

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 *x* * FLT_RADIX^{n}.

If the result would cause overflow, a range error shall occur and these functions shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (according to the sign of *x*) as appropriate for the return type of the function.

If the correct value would cause underflow, and is not representable, a range error may occur, and *scalbln*(), *scalblnf*(), *scalblnl*(), *scalbn*(), *scalbnf*(), and *scalbnl*() shall return 0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, LDBL_MIN, DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

If *x* is NaN, a NaN shall be returned.

If *x* is ±0 or ±Inf, *x* shall be returned.

If *n* is 0, *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.

## Errors

These functions shall fail if:

- Range Error
The result overflows.

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.

These functions 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

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

These functions are named so as to avoid conflicting with the historical definition of the *scalb*() function from the Single UNIX Specification. The difference is that the *scalb*() function has a second argument of **double** instead of **int**. The *scalb*() function is not part of the ISO C standard. The three functions whose second type is **long** are provided because the factor required to scale from the smallest positive floating-point value to the largest finite one, on many implementations, is too large to represent in the minimum-width **int** format.

## Future Directions

None.

## See Also

feclearexcept(), fetestexcept()

The Base Definitions volume of POSIX.1-2017, *Section 4.20*, *Treatment of Error Conditions for Mathematical Functions*, <math.h>

## Copyright

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

## Referenced By

ilogb(3p), logb(3p), math.h(0p).