## table of contents

POW(3) | Linux Programmer's Manual | POW(3) |

# NAME¶

pow, powf, powl - power functions

# SYNOPSIS¶

#include <math.h>

double pow(doublex, doubley);float powf(floatx, floaty);long double powl(long doublex, long doubley);

Link with *-lm*.

**powf**(), **powl**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

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

# DESCRIPTION¶

These functions return the value of *x* raised to the power
of *y*.

# RETURN VALUE¶

On success, these functions return the value of *x* to the
power of *y*.

If *x* is a finite value less than 0, and *y* is a
finite noninteger, a domain error occurs, and a NaN is returned.

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

If result underflows, and is not representable, a range error occurs, and 0.0 is returned.

Except as specified below, if *x* or *y* is a NaN, the
result is a NaN.

If *x* is +1, the result is 1.0 (even if *y* is a
NaN).

If *y* is 0, the result is 1.0 (even if *x* is a
NaN).

If *x* is +0 (-0), and *y* is an odd integer greater
than 0, the result is +0 (-0).

If *x* is 0, and *y* greater than 0 and not an odd
integer, the result is +0.

If *x* is -1, and *y* is positive infinity or negative
infinity, the result is 1.0.

If the absolute value of *x* is less than 1, and *y* is
negative infinity, the result is positive infinity.

If the absolute value of *x* is greater than 1, and *y*
is negative infinity, the result is +0.

If the absolute value of *x* is less than 1, and *y* is
positive infinity, the result is +0.

If the absolute value of *x* is greater than 1, and *y*
is positive infinity, the result is positive infinity.

If *x* is negative infinity, and *y* is an odd integer
less than 0, the result is -0.

If *x* is negative infinity, and *y* less than 0 and not
an odd integer, the result is +0.

If *x* is negative infinity, and *y* is an odd integer
greater than 0, the result is negative infinity.

If *x* is negative infinity, and *y* greater than 0 and
not an odd integer, the result is positive infinity.

If *x* is positive infinity, and *y* less than 0, the
result is +0.

If *x* is positive infinity, and *y* greater than 0, the
result is positive infinity.

If *x* is +0 or -0, and *y* is an odd integer less than
0, a pole error occurs and **HUGE_VAL**, **HUGE_VALF**, or
**HUGE_VALL**, is returned, with the same sign as *x*.

If *x* is +0 or -0, and *y* is less than 0 and not an
odd integer, a pole error occurs and +**HUGE_VAL**, +**HUGE_VALF**, or
+**HUGE_VALL**, 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:

- Domain error:
*x*is negative, and*y*is a finite noninteger *errno*is set to**EDOM**. An invalid floating-point exception (**FE_INVALID**) is raised.- Pole error:
*x*is zero, and*y*is negative *errno*is set to**ERANGE**(but see BUGS). A divide-by-zero floating-point exception (**FE_DIVBYZERO**) is raised.- Range error: the result overflows
*errno*is set to**ERANGE**. An overflow floating-point exception (**FE_OVERFLOW**) is raised.- Range error: the result underflows
*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 |

pow (), powf (), powl () | Thread safety | MT-Safe |

# CONFORMING TO¶

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

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

# BUGS¶

## Historical bugs (now fixed)¶

Before glibc 2.28, on some architectures (e.g., x86-64)
**pow**() may be more than 10,000 times slower for some inputs than for
other nearby inputs. This affects only **pow**(), and not **powf**()
nor **powl**(). This problem was fixed in glibc 2.28.

A number of bugs in the glibc implementation of **pow**() were
fixed in glibc version 2.16.

In glibc 2.9 and earlier, when a pole error occurs, *errno*
is set to **EDOM** instead of the POSIX-mandated **ERANGE**. Since
version 2.10, glibc does the right thing.

In version 2.3.2 and earlier, when an overflow or underflow error
occurs, glibc's **pow**() generates a bogus invalid floating-point
exception (**FE_INVALID**) in addition to the overflow or underflow
exception.

# SEE ALSO¶

# COLOPHON¶

This page is part of release 5.13 of the Linux *man-pages*
project. A description of the project, information about reporting bugs, and
the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.

2021-03-22 |