1POW(3) Linux Programmer's Manual POW(3)
2
6 pow, powf, powl - power functions
7
9 #include <math.h>
10 double pow(double x, double y);
12 float powf(float x, float y);
13 long double powl(long double x, long double y);
14 Link with -lm.
16 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
18 powf(), powl():
20 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
21 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
22 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
23
25 These functions return the value of x raised to the power of y.
26
28 On success, these functions return the value of x to the power of y.
29 If x is a finite value less than 0, and y is a finite noninteger, a
31 domain error occurs, and a NaN is returned.
32 If the result overflows, a range error occurs, and the functions return
34 HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the mathemati‐
35 cally correct sign.
36 If result underflows, and is not representable, a range error occurs,
38 and 0.0 is returned.
39 Except as specified below, if x or y is a NaN, the result is a NaN.
41 If x is +1, the result is 1.0 (even if y is a NaN).
43 If y is 0, the result is 1.0 (even if x is a NaN).
45 If x is +0 (-0), and y is an odd integer greater than 0, the result is
47 +0 (-0).
48 If x is 0, and y greater than 0 and not an odd integer, the result is
50 +0.
51 If x is -1, and y is positive infinity or negative infinity, the result
53 is 1.0.
54 If the absolute value of x is less than 1, and y is negative infinity,
56 the result is positive infinity.
57 If the absolute value of x is greater than 1, and y is negative infin‐
59 ity, the result is +0.
60 If the absolute value of x is less than 1, and y is positive infinity,
62 the result is +0.
63 If the absolute value of x is greater than 1, and y is positive infin‐
65 ity, the result is positive infinity.
66 If x is negative infinity, and y is an odd integer less than 0, the
68 result is -0.
69 If x is negative infinity, and y less than 0 and not an odd integer,
71 the result is +0.
72 If x is negative infinity, and y is an odd integer greater than 0, the
74 result is negative infinity.
75 If x is negative infinity, and y greater than 0 and not an odd integer,
77 the result is positive infinity.
78 If x is positive infinity, and y less than 0, the result is +0.
80 If x is positive infinity, and y greater than 0, the result is positive
82 infinity.
83 If x is +0 or -0, and y is an odd integer less than 0, a pole error
85 occurs and HUGE_VAL, HUGE_VALF, or HUGE_VALL, is returned, with the
86 same sign as x.
87 If x is +0 or -0, and y is less than 0 and not an odd integer, a pole
89 error occurs and +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, is returned.
90
92 See math_error(7) for information on how to determine whether an error
93 has occurred when calling these functions.
94 The following errors can occur:
96 Domain error: x is negative, and y is a finite noninteger
98 errno is set to EDOM. An invalid floating-point exception
99 (FE_INVALID) is raised.
100 Pole error: x is zero, and y is negative
102 errno is set to ERANGE (but see BUGS). A divide-by-zero float‐
103 ing-point exception (FE_DIVBYZERO) is raised.
104 Range error: the result overflows
106 errno is set to ERANGE. An overflow floating-point exception
107 (FE_OVERFLOW) is raised.
108 Range error: the result underflows
110 errno is set to ERANGE. An underflow floating-point exception
111 (FE_UNDERFLOW) is raised.
112
114 For an explanation of the terms used in this section, see
115 attributes(7).
116 ┌──────────────────────┬───────────────┬─────────┐
118 │Interface │ Attribute │ Value │
119 ├──────────────────────┼───────────────┼─────────┤
120 │pow(), powf(), powl() │ Thread safety │ MT-Safe │
121 └──────────────────────┴───────────────┴─────────┘
123 C99, POSIX.1-2001, POSIX.1-2008.
124 The variant returning double also conforms to SVr4, 4.3BSD, C89.
126
128 On 64-bits, pow() may be more than 10,000 times slower for some (rare)
129 inputs than for other nearby inputs. This affects only pow(), and not
130 powf() nor powl().
131 In glibc 2.9 and earlier, when a pole error occurs, errno is set to
133 EDOM instead of the POSIX-mandated ERANGE. Since version 2.10, glibc
134 does the right thing.
135 If x is negative, then large negative or positive y values yield a NaN
137 as the function result, with errno set to EDOM, and an invalid
138 (FE_INVALID) floating-point exception. For example, with pow(), one
139 sees this behavior when the absolute value of y is greater than about
140 9.223373e18.
141 In version 2.3.2 and earlier, when an overflow or underflow error
143 occurs, glibc's pow() generates a bogus invalid floating-point excep‐
144 tion (FE_INVALID) in addition to the overflow or underflow exception.
145
147 cbrt(3), cpow(3), sqrt(3)
148
150 This page is part of release 5.02 of the Linux man-pages project. A
151 description of the project, information about reporting bugs, and the
152 latest version of this page, can be found at
153 https://www.kernel.org/doc/man-pages/.
154 2017-09-15 POW(3)