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man:powf

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():
         _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
             || /* Since glibc 2.19: */ _DEFAULT_SOURCE
             || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

     These functions return 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 mathemati-
     cally 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 infin-
     ity, 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 infin-
     ity, 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  float-
            ing-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.

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     allbox; lbw21 lb lb l l l.  Interface Attribute Value T{ pow(), powf(),
     powl() T}   Thread safety  MT-Safe

CONFORMING TO

     C99, POSIX.1-2001, POSIX.1-2008.
     The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS

     On  64-bits, pow() may be more than 10,000 times slower for some (rare)
     inputs than for other nearby inputs.  This affects only pow(), and  not
     powf() nor powl().
     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  excep-
     tion (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 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.
                                2017-09-15                            POW(3)
/data/webs/external/dokuwiki/data/pages/man/powf.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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