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.
10

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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DESCRIPTION

22       The functionality described on this reference page is aligned with  the
23       ISO C  standard.  Any  conflict between the requirements described here
24       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
25       defers to the ISO C standard.
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27       These functions shall compute loge(1.0 + x).
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29       An  application  wishing to check for error situations should set errno
30       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
31       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
32       FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero,  an  error  has
33       occurred.
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RETURN VALUE

36       Upon  successful  completion,  these functions shall return the natural
37       logarithm of 1.0 + x.
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39       If x is -1, a  pole  error  shall  occur  and  log1p(),  log1pf(),  and
40       log1pl()  shall  return  -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respec‐
41       tively.
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43       For finite values of x that are less than -1, or if x is -Inf, a domain
44       error  shall  occur, and either a NaN (if supported), or an implementa‐
45       tion-defined value shall be returned.
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47       If x is NaN, a NaN shall be returned.
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49       If x is ±0, or +Inf, x shall be returned.
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51       If x is subnormal, a range error may occur
52       and x should be returned.
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54       If x is not returned, log1p(), log1pf(), and log1pl() shall  return  an
55       implementation-defined  value  no  greater  in  magnitude than DBL_MIN,
56       FLT_MIN, and LDBL_MIN, respectively.
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ERRORS

59       These functions shall fail if:
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61       Domain Error
62                   The finite value of x is less than -1, or x is -Inf.
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64                   If the integer expression (math_errhandling  &  MATH_ERRNO)
65                   is  non-zero,  then  errno  shall be set to [EDOM].  If the
66                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
67                   non-zero,  then  the invalid floating-point exception shall
68                   be raised.
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70       Pole Error  The value of x is -1.
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72                   If the integer expression (math_errhandling  &  MATH_ERRNO)
73                   is  non-zero,  then errno shall be set to [ERANGE].  If the
74                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
75                   non-zero,  then the divide-by-zero floating-point exception
76                   shall be raised.
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78       These functions may fail if:
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80       Range Error The value of x is subnormal.
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82                   If the integer expression (math_errhandling  &  MATH_ERRNO)
83                   is  non-zero,  then errno shall be set to [ERANGE].  If the
84                   integer expression (math_errhandling &  MATH_ERREXCEPT)  is
85                   non-zero, then the underflow floating-point exception shall
86                   be raised.
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88       The following sections are informative.
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EXAMPLES

91       None.
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APPLICATION USAGE

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

99       None.
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FUTURE DIRECTIONS

102       None.
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SEE ALSO

105       feclearexcept(), fetestexcept(), log()
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107       The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
108       Error Conditions for Mathematical Functions, <math.h>
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111       Portions  of  this text are reprinted and reproduced in electronic form
112       from IEEE Std 1003.1-2017, Standard for Information Technology --  Por‐
113       table  Operating System Interface (POSIX), The Open Group Base Specifi‐
114       cations Issue 7, 2018 Edition, Copyright (C) 2018 by the  Institute  of
115       Electrical  and  Electronics Engineers, Inc and The Open Group.  In the
116       event of any discrepancy between this version and the original IEEE and
117       The  Open Group Standard, the original IEEE and The Open Group Standard
118       is the referee document. The original Standard can be  obtained  online
119       at http://www.opengroup.org/unix/online.html .
120
121       Any  typographical  or  formatting  errors that appear in this page are
122       most likely to have been introduced during the conversion of the source
123       files  to  man page format. To report such errors, see https://www.ker‐
124       nel.org/doc/man-pages/reporting_bugs.html .
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128IEEE/The Open Group                  2017                            LOG1P(3P)
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