1LOG(3)                     Linux Programmer's Manual                    LOG(3)
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NAME

6       log, logf, logl - natural logarithmic function
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SYNOPSIS

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

25       These functions return the natural logarithm of x.
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RETURN VALUE

28       On success, these functions return the natural logarithm of x.
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30       If x is a NaN, a NaN is returned.
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32       If x is 1, the result is +0.
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34       If x is positive infinity, positive infinity is returned.
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36       If  x  is  zero,  then  a  pole  error occurs, and the functions return
37       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
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39       If x is negative (including negative infinity),  then  a  domain  error
40       occurs, and a NaN (not a number) is returned.
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ERRORS

43       See  math_error(7) for information on how to determine whether an error
44       has occurred when calling these functions.
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46       The following errors can occur:
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48       Domain error: x is negative
49              errno is set  to  EDOM.   An  invalid  floating-point  exception
50              (FE_INVALID) is raised.
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52       Pole error: x is zero
53              errno  is set to ERANGE.  A divide-by-zero floating-point excep‐
54              tion (FE_DIVBYZERO) is raised.
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ATTRIBUTES

57       For  an  explanation  of  the  terms  used   in   this   section,   see
58       attributes(7).
59
60       ┌──────────────────────┬───────────────┬─────────┐
61       │Interface             │ Attribute     │ Value   │
62       ├──────────────────────┼───────────────┼─────────┤
63       │log(), logf(), logl() │ Thread safety │ MT-Safe │
64       └──────────────────────┴───────────────┴─────────┘

CONFORMING TO

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

71       In  glibc  2.5  and earlier, taking the log() of a NaN produces a bogus
72       invalid floating-point (FE_INVALID) exception.
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SEE ALSO

75       cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)
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COLOPHON

78       This page is part of release 5.02 of the Linux  man-pages  project.   A
79       description  of  the project, information about reporting bugs, and the
80       latest    version    of    this    page,    can     be     found     at
81       https://www.kernel.org/doc/man-pages/.
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85                                  2017-09-15                            LOG(3)
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