log1pl(3)

1log1p(3)                   Library Functions Manual                   log1p(3)
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NAME

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

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       double log1p(double x);
15       float log1pf(float x);
16       long double log1pl(long double x);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       log1p():
21           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
22               || _XOPEN_SOURCE >= 500
23               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
24               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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26       log1pf(), log1pl():
27           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
28               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
29               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

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

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

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

67       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
68       tributes(7).
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70       ┌────────────────────────────────────────────┬───────────────┬─────────┐
71       │Interface                                   │ Attribute     │ Value   │
72       ├────────────────────────────────────────────┼───────────────┼─────────┤
73       │log1p(), log1pf(), log1pl()                 │ Thread safety │ MT-Safe │
74       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

77       C11, POSIX.1-2008.
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HISTORY

80       C99, POSIX.1-2001.
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BUGS

83       Before glibc 2.22, the glibc implementation did not set errno  to  EDOM
84       when a domain error occurred.
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86       Before glibc 2.22, the glibc implementation did not set errno to ERANGE
87       when a range error occurred.
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