1LGAMMA(3P)                 POSIX Programmer's Manual                LGAMMA(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       lgamma, lgammaf, lgammal - log gamma function
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SYNOPSIS

15       #include <math.h>
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17       double lgamma(double x);
18       float lgammaf(float x);
19       long double lgammal(long double x);
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22       extern int signgam;
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DESCRIPTION

26       These functions shall compute
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29       The argument x need not be a non-positive integer (Gamma(x) is  defined
30       over the reals, except the non-positive integers).
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32       The sign of Gamma(x) is returned in the external integer signgam.
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34       These  functions need not be reentrant. A function that is not required
35       to be reentrant is not required to be thread-safe.
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37       An application wishing to check for error situations should  set  errno
38       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
39       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
40       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
41       occurred.
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RETURN VALUE

44       Upon successful completion, these functions shall return the  logarith‐
45       mic gamma of x.
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47       If  x is a non-positive integer, a pole error shall occur and lgamma(),
48       lgammaf(),  and  lgammal()  shall  return  +HUGE_VAL,  +HUGE_VALF,  and
49       +HUGE_VALL, respectively.
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51       If  the  correct  value would cause overflow, a range error shall occur
52       and  lgamma(),  lgammaf(),  and  lgammal()  shall   return   ±HUGE_VAL,
53       ±HUGE_VALF, and ±HUGE_VALL (having the same sign as the correct value),
54       respectively.
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56       If x is NaN, a NaN shall be returned.
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58       If x is 1 or 2, +0 shall be returned.
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60       If x is ±Inf, +Inf shall be returned.
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ERRORS

63       These functions shall fail if:
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65       Pole Error
66              The x argument is a negative integer or zero.
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68       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
69       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
70       (math_errhandling & MATH_ERREXCEPT) is non-zero,  then  the  divide-by-
71       zero floating-point exception shall be raised.
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73       Range Error
74              The result overflows.
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76       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
77       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
78       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then the overflow
79       floating-point exception shall be raised.
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82       The following sections are informative.
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EXAMPLES

85       None.
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APPLICATION USAGE

88       On  error,  the  expressions  (math_errhandling   &   MATH_ERRNO)   and
89       (math_errhandling  & MATH_ERREXCEPT) are independent of each other, but
90       at least one of them must be non-zero.
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RATIONALE

93       None.
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FUTURE DIRECTIONS

96       None.
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SEE ALSO

99       exp(), feclearexcept(), fetestexcept(), isnan(), the  Base  Definitions
100       volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Condi‐
101       tions for Mathematical Functions, <math.h>
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104       Portions of this text are reprinted and reproduced in  electronic  form
105       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
106       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
107       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
108       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
109       event of any discrepancy between this version and the original IEEE and
110       The Open Group Standard, the original IEEE and The Open Group  Standard
111       is  the  referee document. The original Standard can be obtained online
112       at http://www.opengroup.org/unix/online.html .
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116IEEE/The Open Group                  2003                           LGAMMA(3P)
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