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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*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

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

# 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¶

On 64-bits,**pow**() may be more than 10,000 times slower for some (rare) inputs than for other nearby inputs. This affects only

**pow**(), and not

**powf**() nor

**powl**().

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.

If *x* is negative, then large negative or positive *y*
values yield a NaN as the function result, with *errno* set to
**EDOM**, and an invalid (**FE_INVALID**) floating-point exception.
For example, with **pow**(), one sees this behavior when the absolute
value of *y* is greater than about 9.223373e18.

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¶

cbrt(3), cpow(3), sqrt(3)# COLOPHON¶

This page is part of release 4.10 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/.

2016-03-15 |