1LOG1P(3)                   Linux Programmer's Manual                  LOG1P(3)
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NAME

6       log1p, log1pf, log1pl -  logarithm of 1 plus argument
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SYNOPSIS

9       #include <math.h>
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11       double log1p(double x);
12       float log1pf(float x);
13       long double log1pl(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       log1p():
20           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
21               || _XOPEN_SOURCE >= 500
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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25       log1pf(), log1pl():
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
27               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
28               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

31       These functions return a value equivalent to
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33           log (1 + x)
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35       The result is computed in a way that is accurate even if the value of x
36       is near zero.
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RETURN VALUE

39       On success, these functions return the natural logarithm of (1 + x).
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41       If x is a NaN, a NaN is returned.
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43       If x is positive infinity, positive infinity is returned.
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45       If x is -1, a pole error occurs, and the  functions  return  -HUGE_VAL,
46       -HUGE_VALF, or -HUGE_VALL, respectively.
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48       If  x is less than -1 (including negative infinity), a domain error oc‐
49       curs, and a NaN (not a number) is returned.
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ERRORS

52       See math_error(7) for information on how to determine whether an  error
53       has occurred when calling these functions.
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55       The following errors can occur:
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57       Domain error: x is less than -1
58              errno  is set to EDOM (but see BUGS).  An invalid floating-point
59              exception (FE_INVALID) is raised.
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61       Pole error: x is -1
62              errno is set to ERANGE (but see BUGS).  A divide-by-zero  float‐
63              ing-point exception (FE_DIVBYZERO) is raised.
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ATTRIBUTES

66       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
67       tributes(7).
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69       ┌────────────────────────────────────────────┬───────────────┬─────────┐
70       │Interface                                   │ Attribute     │ Value   │
71       ├────────────────────────────────────────────┼───────────────┼─────────┤
72       │log1p(), log1pf(), log1pl()                 │ Thread safety │ MT-Safe │
73       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

76       C99, POSIX.1-2001, POSIX.1-2008.
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BUGS

79       Before version 2.22, the glibc implementation did not set errno to EDOM
80       when a domain error occurred.
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82       Before  version  2.22,  the  glibc  implementation did not set errno to
83       ERANGE when a range error occurred.
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SEE ALSO

86       exp(3), expm1(3), log(3)
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COLOPHON

89       This page is part of release 5.12 of the Linux  man-pages  project.   A
90       description  of  the project, information about reporting bugs, and the
91       latest    version    of    this    page,    can     be     found     at
92       https://www.kernel.org/doc/man-pages/.
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96                                  2021-03-22                          LOG1P(3)
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