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Copyright

pow, powf, powl - power function

#include <math.h>

double pow(doublex, doubley);

float powf(floatx, floaty);

long double powl(long doublex, long doubley);

These functions shall compute the value of

xraised to the powery,x**y. Ifxis 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 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 either 0.0 (if supported), or an implementation-defined value shall be returned.

If

xoryis 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.For

yan odd integer < 0, ifxis ±0, a pole error shall occur and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL shall be returned forpow(),powf(), andpowl(), respectively.For

y< 0 and not an odd integer, ifxis ±0, a pole error shall occur and HUGE_VAL, HUGE_VALF, and HUGE_VALL shall be returned forpow(),powf(), andpowl(), respectively.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:

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then

Domain Error The value of xis negative andyis a finite non-integer.If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errnoshall 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 xis zero andyis negative.If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errnoshall 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 errnoshall 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: Range Error The result underflows. errnoshall 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.

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() ,isnan() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions,<math.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE/The Open Group |
POW (P) | 2003 |