# ldexp man page

ldexp, ldexpf, ldexpl — multiply floating-point number by integral power of 2

## Synopsis

**#include <math.h>**
**double ldexp(double** *x***, int** *exp***);**
**float ldexpf(float** *x***, int** *exp***);**
**long double ldexpl(long double** *x***, int** *exp***);**

`Link with `

*-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):**ldexpf**(), **ldexpl**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

## Description

These functions return the result of multiplying the floating-point number *x* by 2 raised to the power *exp*.

## Return Value

On success, these functions return *x * (2^exp)*.

If *exp* is zero, then *x* is returned.

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

If *x* is positive infinity (negative infinity), positive infinity (negative infinity) is returned.

If the result underflows, a range error occurs, and zero is returned.

If the result overflows, a range error occurs, and the functions return **HUGE_VAL**, **HUGE_VALF**, or **HUGE_VALL**, respectively, with a sign the same as *x*.

## 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:

- Range error, overflow
*errno*is set to**ERANGE**. An overflow floating-point exception (**FE_OVERFLOW**) is raised.- Range error, underflow
*errno*is set to**ERANGE**. An underflow floating-point exception (**FE_UNDERFLOW**) is raised.

## Attributes

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |
---|---|---|

ldexp(), ldexpf(), ldexpl() | Thread safety | MT-Safe |

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

## See Also

## Colophon

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## Referenced By

frexp(3), modf(3), scalb(3), scalbln(3).

ldexpf(3) and ldexpl(3) are aliases of ldexp(3).