1LOG(3) Linux Programmer's Manual LOG(3)
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6 log, logf, logl - natural logarithmic function
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9 #include <math.h>
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11 double log(double x);
12 float logf(float x);
13 long double logl(long double x);
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15 Link with -lm.
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17 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19 logf(), logl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
20 _ISOC99_SOURCE; or cc -std=c99
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23 The log() function returns the natural logarithm of x.
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26 On success, these functions return the natural logarithm of x.
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28 If x is a NaN, a NaN is returned.
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30 If x is 1, the result is +0.
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32 If x is positive infinity, positive infinity is returned.
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34 If x is zero, then a pole error occurs, and the functions return
35 -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
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37 If x is negative (including negative infinity), then a domain error
38 occurs, and a NaN (not a number) is returned.
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41 See math_error(7) for information on how to determine whether an error
42 has occurred when calling these functions.
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44 The following errors can occur:
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46 Domain error: x is negative
47 errno is set to EDOM. An invalid floating-point exception
48 (FE_INVALID) is raised.
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50 Pole error: x is zero
51 errno is set to ERANGE. A divide-by-zero floating-point excepâ
52 tion (FE_DIVBYZERO) is raised.
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55 C99, POSIX.1-2001. The variant returning double also conforms to SVr4,
56 4.3BSD, C89.
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59 In glibc 2.5 and earlier, taking the log() of a NaN produces a bogus
60 invalid floating-point (FE_INVALID) exception.
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63 cbrt(3), clog(3), log1p(3), sqrt(3)
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66 This page is part of release 3.22 of the Linux man-pages project. A
67 description of the project, and information about reporting bugs, can
68 be found at http://www.kernel.org/doc/man-pages/.
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72 2008-08-10 LOG(3)