POW(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():
           _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 do-
       main 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 re-
       sult 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 oc-
       curs 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 at-
       tributes(7).

       +----------------------+---------------+---------+
       |Interface             | Attribute     | Value   |
       +----------------------+---------------+---------+
       |pow(), powf(), powl() | 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
   Historical bugs (now fixed)
       Before glibc 2.28, on some architectures (e.g., x86-64)  pow()  may  be
       more than 10,000 times slower for some inputs than for other nearby in-
       puts.  This affects only pow(), and not powf() nor powl().  This  prob-
       lem was fixed in glibc 2.28.

       A  number  of  bugs  in the glibc implementation of pow() were fixed in
       glibc version 2.16.

       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.

       In version 2.3.2 and earlier, when an overflow or underflow  error  oc-
       curs,  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 5.07 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/.

                                  2020-06-09                            POW(3)

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