IEEE Std 1003.1-2008

Copyright © 2001-2008 The IEEE and The Open Group

pow, powf, powl - power function

#include <math.h>

double pow(doublex, doubley);

float powf(floatx, floaty);

long double powl(long doublex, long doubley);

^{[CX]}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.1-2008 defers to the ISO C standard.These functions shall compute the value of

xraised to the powery,x. If^{y}xis negative, the application shall ensure thatyis an integer value.An application wishing to check for error situations should set

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the value of

xraised to the powery.For finite values of

x< 0, and finite non-integer values ofy, a domain error shall occur and^{[MX]}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(), andpowl() 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

^{[MX]}either 0.0 (if supported), or an implementation-defined value shall be returned.For

y< 0, ifxis zero, a^{[CX]}pole error may occur andpow(),powf(), andpowl() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively.^{[MX]}On systems that support the IEC 60559 Floating-Point option, a pole error shall occur andpow(),powf(), andpowl() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively ifyis an odd integer, or HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively ifyis not an odd integer.

^{[MX]}Ifxoryis a NaN, a NaN shall be returned (unless specified elsewhere in this description).For any value of

y(including NaN), ifxis +1, 1.0 shall be returned.For any value of

x(including NaN), ifyis ±0, 1.0 shall be returned.For any odd integer value of

y> 0, ifxis ±0, ±0 shall be returned.For

y> 0 and not an odd integer, ifxis ±0, +0 shall be returned.If

xis -1, andyis ±Inf, 1.0 shall be returned.For |

x| < 1, ifyis -Inf, +Inf shall be returned.For |

x| > 1, ifyis -Inf, +0 shall be returned.For |

x| < 1, ifyis +Inf, +0 shall be returned.For |

x| > 1, ifyis +Inf, +Inf shall be returned.For

yan odd integer < 0, ifxis -Inf, -0 shall be returned.For

y< 0 and not an odd integer, ifxis -Inf, +0 shall be returned.For

yan odd integer > 0, ifxis -Inf, -Inf shall be returned.For

y> 0 and not an odd integer, ifxis -Inf, +Inf shall be returned.For

y< 0, ifxis +Inf, +0 shall be returned.For

y> 0, ifxis +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.

These functions shall fail if:

- Domain Error
- The value of
xis negative andyis a finite non-integer.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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
^{[MX]}The value ofxis zero andyis negative.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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, thenerrnoshall 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
xis zero andyis negative.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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, thenerrnoshall be set to [ERANGE]. If the integer expression (math_errhandling& MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

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.

None.

None.

exp,feclearexcept,fetestexcept,isnanXBD

Treatment of Error Conditions for Mathematical Functions,<math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The normative text is updated to avoid use of the term "must" for application requirements.

The

powf() andpowl() functions are added for alignment with the ISO/IEC 9899:1999 standard.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/42 is applied, correcting the third paragraph in the RETURN VALUE section.

ISO/IEC 9899:1999 standard, Technical Corrigendum 2 #51 (SD5-XSH-ERN-81) is applied.

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