1LOG1P(P)                   POSIX Programmer's Manual                  LOG1P(P)
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NAME

6       log1p, log1pf, log1pl - compute a natural logarithm
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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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DESCRIPTION

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

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

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

77       None.
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APPLICATION USAGE

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

85       None.
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FUTURE DIRECTIONS

88       None.
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SEE ALSO

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