# Manpage of POW

# POW

Section: Linux Programmer's Manual (3)Updated: 2016-03-15

Index

## 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**():

- _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 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)

## Index

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