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Linux 2.6 - man page for powl (linux section 3)

POW(3)							     Linux Programmer's Manual							    POW(3)

NAME
pow, powf, powl - power functions
SYNOPSIS
#include <math.h> double pow(double x, double y); float powf(float x, float y); long double powl(long double x, long double y); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): powf(), powl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
DESCRIPTION
The pow() function returns the value of x raised to the power of y.
RETURN VALUE
On success, these functions return the value of x to the power of y. If x is a finite value less than 0, and y is a finite noninteger, a domain error occurs, and a NaN is returned. If the result overflows, a range error occurs, and the functions return HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathemat- ically correct sign. If result underflows, and is not representable, a range error occurs, and 0.0 is returned. Except as specified below, if x or y is a NaN, the result is a NaN. If x is +1, the result is 1.0 (even if y is a NaN). If y is 0, the result is 1.0 (even if x is a NaN). If x is +0 (-0), and y is an odd integer greater than 0, the result is +0 (-0). If x is 0, and y greater than 0 and not an odd integer, the result is +0. If x is -1, and y is positive infinity or negative infinity, the result is 1.0. If the absolute value of x is less than 1, and y is negative infinity, the result is positive infinity. If the absolute value of x is greater than 1, and y is negative infinity, the result is +0. If the absolute value of x is less than 1, and y is positive infinity, the result is +0. If the absolute value of x is greater than 1, and y is positive infinity, the result is positive infinity. If x is negative infinity, and y is an odd integer less than 0, the result is -0. If x is negative infinity, and y less than 0 and not an odd integer, the result is +0. If x is negative infinity, and y is an odd integer greater than 0, the result is negative infinity. If x is negative infinity, and y greater than 0 and not an odd integer, the result is positive infinity. If x is positive infinity, and y less than 0, the result is +0. If x is positive infinity, and y greater than 0, the result is positive infinity. If x is +0 or -0, and y is an odd integer less than 0, a pole error occurs and HUGE_VAL, HUGE_VALF, or HUGE_VALL, is returned, with the same sign as x. If x is +0 or -0, and y is less than 0 and not an odd integer, a pole error occurs and +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, is returned.
ERRORS
See math_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur: Domain error: x is negative, and y is a finite noninteger errno is set to EDOM. An invalid floating-point exception (FE_INVALID) is raised. Pole error: x is zero, and y is negative errno is set to ERANGE (but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised. Range error: the result overflows errno is set to ERANGE. An overflow floating-point exception (FE_OVERFLOW) is raised. Range error: the result underflows errno is set to ERANGE. An underflow floating-point exception (FE_UNDERFLOW) is raised.
CONFORMING TO
C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
BUGS
In glibc 2.9 and earlier, when a pole error occurs, errno is set to EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc does the right thing. If x is negative, then large negative or positive y values yield a NaN as the function result, with errno set to EDOM, and an invalid (FE_INVALID) floating-point exception. For example, with pow(), one sees this behavior when the absolute value of y is greater than about 9.223373e18. In version 2.3.2 and earlier, when an overflow or underflow error occurs, glibc's pow() generates a bogus invalid floating-point exception (FE_INVALID) in addition to the overflow or underflow exception.
SEE ALSO
cbrt(3), cpow(3), sqrt(3)
COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2010-09-12 POW(3)