Originální popis anglicky:
pow, powf, powl - power function
Návod, kniha: POSIX Programmer's Manual
#include <math.h>
double pow(double
x, double
y);
float powf(float
x, float
y);
long double powl(long double
x, long double
y);
These functions shall compute the value of
x raised to the power
y,
x**y. 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.
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 either 0.0 (if supported), or an
implementation-defined value shall be returned.
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.
For
y an odd integer < 0, if
x is ±0, a pole error shall
occur and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL shall be
returned for
pow(),
powf(), and
powl(), respectively.
For
y < 0 and not an odd integer, if
x is ±0, a pole
error shall occur and HUGE_VAL, HUGE_VALF, and HUGE_VALL shall be returned for
pow(),
powf(), and
powl(), 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:
- 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:
- 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.
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
.
