##
table of contents

POW(3P) | POSIX Programmer's Manual | POW(3P) |

# 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.

# NAME¶

pow, powf, powl — power function

# SYNOPSIS¶

#include <math.h>

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

# 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 the value of *x* raised to the
power *y*, *xy*. If *x* is negative, the application shall
ensure that *y* is an integer value.

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 the value
of *x* raised to the power *y*.

For finite values of *x* < 0, and finite non-integer
values of *y*, a domain error shall occur and either a NaN (if
representable), or an implementation-defined value shall be returned.

If the correct value would cause overflow, a range error shall
occur and *pow*(), *powf*(), and *powl*() shall return
±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively,
with the same sign as the correct value of the function.

If the correct value would cause underflow, and is not
representable, a range error may occur, and *pow*(), *powf*(), and
*powl*() 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, and LDBL_MIN, respectively.

For *y* < 0, if *x* is zero, a pole error may occur
and *pow*(), *powf*(), and *powl*() shall return
±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively. On
systems that support the IEC 60559 Floating-Point option, if *x* is
±0, a pole error shall occur and *pow*(), *powf*(), and
*powl*() shall return ±HUGE_VAL, ±HUGE_VALF, and
±HUGE_VALL, respectively if *y* is an odd integer, or HUGE_VAL,
HUGE_VALF, and HUGE_VALL, respectively if *y* is not an odd
integer.

If *x* or *y* is a NaN, a NaN shall be returned (unless
specified elsewhere in this description).

For any value of *y* (including NaN), if *x* is +1, 1.0
shall be returned.

For any value of *x* (including NaN), if *y* is
±0, 1.0 shall be returned.

For any odd integer value of *y* > 0, if *x* is
±0, ±0 shall be returned.

For *y* > 0 and not an odd integer, if *x* is
±0, +0 shall be returned.

If *x* is -1, and *y* is ±Inf, 1.0 shall be
returned.

For |*x*| < 1, if *y* is -Inf, +Inf shall be
returned.

For |*x*| > 1, if *y* is -Inf, +0 shall be
returned.

For |*x*| < 1, if *y* is +Inf, +0 shall be
returned.

For |*x*| > 1, if *y* is +Inf, +Inf shall be
returned.

For *y* an odd integer < 0, if *x* is -Inf, -0 shall
be returned.

For *y* < 0 and not an odd integer, if *x* is -Inf,
+0 shall be returned.

For *y* an odd integer > 0, if *x* is -Inf, -Inf
shall be returned.

For *y* > 0 and not an odd integer, if *x* is -Inf,
+Inf shall be returned.

For *y* < 0, if *x* is +Inf, +0 shall be
returned.

For *y* > 0, if *x* is +Inf, +Inf 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:

- Domain Error
- The value of
*x*is negative and*y*is a finite non-integer.

If the integer expression (*math_errhandling* &
MATH_ERRNO) is non-zero, then *errno* shall be set to **[EDOM]**. If
the integer expression (*math_errhandling* & MATH_ERREXCEPT) is
non-zero, then the invalid floating-point exception shall be raised.

- Pole Error
- The value of
*x*is zero and*y*is negative.

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 divide-by-zero floating-point exception shall be
raised.

- 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:

- Pole Error
- The value of
*x*is zero and*y*is negative.

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 divide-by-zero floating-point exception shall be
raised.

- 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¶

None.

# FUTURE DIRECTIONS¶

None.

# SEE ALSO¶

* exp()*,

*,*

*feclearexcept*()*,*

*fetestexcept*()

*isnan*()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 .

2017 | IEEE/The Open Group |