1LOG1P(3P)                  POSIX Programmer's Manual                 LOG1P(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       log1p, log1pf, log1pl - compute a natural logarithm
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SYNOPSIS

15       #include <math.h>
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17       double log1p(double x);
18       float log1pf(float x);
19       long double log1pl(long double x);
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21

DESCRIPTION

23       These functions shall compute log_e(1.0 + x).
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25       An application wishing to check for error situations should  set  errno
26       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
27       functions.  On return, if errno is non-zero or  fetestexcept(FE_INVALID
28       |  FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
29       occurred.
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RETURN VALUE

32       Upon successful completion, these functions shall  return  the  natural
33       logarithm of 1.0 + x.
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35       If  x  is  -1,  a  pole  error  shall  occur and log1p(), log1pf(), and
36       log1pl() shall return -HUGE_VAL, -HUGE_VALF,  and  -HUGE_VALL,  respec‐
37       tively.
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39       For  finite  values  of  x  that are less than -1,  or if x is -Inf,  a
40       domain error shall occur, and  either  a  NaN  (if  supported),  or  an
41       implementation-defined value shall be returned.
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43       If x is NaN, a NaN shall be returned.
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45       If x is ±0, or +Inf, x shall be returned.
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47       If x is subnormal, a range error may occur and x should be returned.
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ERRORS

50       These functions shall fail if:
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52       Domain Error
53              The finite value of x is less than -1,  or x is -Inf.
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55       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
56       then  errno  shall  be  set  to  [EDOM].  If  the  integer   expression
57       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero,  then  the invalid
58       floating-point exception shall be raised.
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60       Pole Error
61              The value of x is -1.
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63       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
64       then  errno  shall  be  set  to  [ERANGE].  If  the  integer expression
65       (math_errhandling & MATH_ERREXCEPT) is non-zero,  then  the  divide-by-
66       zero floating-point exception shall be raised.
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69       These functions may fail if:
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71       Range Error
72              The value of x is subnormal.
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74       If  the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
75       then errno  shall  be  set  to  [ERANGE].  If  the  integer  expression
76       (math_errhandling  &  MATH_ERREXCEPT)  is  non-zero, then the underflow
77       floating-point exception shall be raised.
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80       The following sections are informative.
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EXAMPLES

83       None.
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APPLICATION USAGE

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

91       None.
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FUTURE DIRECTIONS

94       None.
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SEE ALSO

97       feclearexcept(), fetestexcept(), log(), the Base Definitions volume  of
98       IEEE Std 1003.1-2001,  Section  4.18, Treatment of Error Conditions for
99       Mathematical Functions, <math.h>
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102       Portions of this text are reprinted and reproduced in  electronic  form
103       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
104       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
105       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
106       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
107       event of any discrepancy between this version and the original IEEE and
108       The Open Group Standard, the original IEEE and The Open Group  Standard
109       is  the  referee document. The original Standard can be obtained online
110       at http://www.opengroup.org/unix/online.html .
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114IEEE/The Open Group                  2003                            LOG1P(3P)
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