#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, 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.
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.
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.
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.
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:
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.
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.
The Base Definitions volume of POSIX.1-2008, Section 4.19, Treatment of Error Conditions for Mathematical Functions, <math.h>
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