lgamma_r(3)

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

6       lgamma, lgammaf, lgammal, lgamma_r, lgammaf_r, lgammal_r, signgam - log
7       gamma function
8

LIBRARY

10       Math library (libm, -lm)
11

SYNOPSIS

13       #include <math.h>
14
15       double lgamma(double x);
16       float lgammaf(float x);
17       long double lgammal(long double x);
18
19       double lgamma_r(double x, int *signp);
20       float lgammaf_r(float x, int *signp);
21       long double lgammal_r(long double x, int *signp);
22
23       extern int signgam;
24
25   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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27       lgamma():
28           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE
29               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
30               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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32       lgammaf(), lgammal():
33           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
34               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
35               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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37       lgamma_r(), lgammaf_r(), lgammal_r():
38           /* Since glibc 2.19: */ _DEFAULT_SOURCE
39               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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41       signgam:
42           _XOPEN_SOURCE
43               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
44               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

47       For the definition of the Gamma function, see tgamma(3).
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49       The lgamma(), lgammaf(), and lgammal()  functions  return  the  natural
50       logarithm of the absolute value of the Gamma function.  The sign of the
51       Gamma function is returned in the external integer signgam declared  in
52       <math.h>.  It is 1 when the Gamma function is positive or zero, -1 when
53       it is negative.
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55       Since using a constant location signgam is not thread-safe,  the  func‐
56       tions  lgamma_r(),  lgammaf_r(),  and lgammal_r() have been introduced;
57       they return the sign via the argument signp.
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RETURN VALUE

60       On success, these functions return the natural logarithm of Gamma(x).
61
62       If x is a NaN, a NaN is returned.
63
64       If x is 1 or 2, +0 is returned.
65
66       If x is positive infinity or negative infinity,  positive  infinity  is
67       returned.
68
69       If  x  is a nonpositive integer, a pole error occurs, and the functions
70       return +HUGE_VAL, +HUGE_VALF, or +HUGE_VALL, respectively.
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72       If the result overflows, a range error occurs, and the functions return
73       HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with the correct math‐
74       ematical sign.
75

ERRORS

77       See math_error(7) for information on how to determine whether an  error
78       has occurred when calling these functions.
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80       The following errors can occur:
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82       Pole error: x is a nonpositive integer
83              errno  is set to ERANGE (but see BUGS).  A divide-by-zero float‐
84              ing-point exception (FE_DIVBYZERO) is raised.
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86       Range error: result overflow
87              errno is set to ERANGE.  An  overflow  floating-point  exception
88              (FE_OVERFLOW) is raised.
89

STANDARDS

91       lgamma()
92       lgammaf()
93       lgammal()
94              C11, POSIX.1-2008.
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96       signgam
97              POSIX.1-2008.
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99       lgamma_r()
100       lgammaf_r()
101       lgammal_r()
102              None.
103

HISTORY

105       lgamma()
106       lgammaf()
107       lgammal()
108              C99, POSIX.1-2001.
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110       signgam
111              POSIX.1-2001.
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113       lgamma_r()
114       lgammaf_r()
115       lgammal_r()
116              None.
117

BUGS

119       In  glibc  2.9  and  earlier, when a pole error occurs, errno is set to
120       EDOM; instead of the POSIX-mandated ERANGE.  Since  glibc  2.10,  glibc
121       does the right thing.
122