man3/log1p.3

   1 .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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  27 .\" Modified 2002-07-27 by Walter Harms
  28 .\"     (walter.harms@informatik.uni-oldenburg.de)
  29 .TH LOG1P 3   2017-09-15 "" "Linux Programmer's Manual"
  30 .SH NAME
  31 log1p, log1pf, log1pl \-  logarithm of 1 plus argument
  32 .SH SYNOPSIS
  33 .nf
  34 .B #include <math.h>
  35 .PP
  36 .BI "double log1p(double " x );
  37 .BI "float log1pf(float " x );
  38 .BI "long double log1pl(long double " x );
  39 .PP
  40 .fi
  41 Link with \fI\-lm\fP.
  42 .PP
  43 .in -4n
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .in
  47 .PP
  48 .ad l
  49 .BR log1p ():
  50 .RS 4
  51 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  52     || _XOPEN_SOURCE\ >=\ 500
  53 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  54     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  55     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  56 .RE
  57 .br
  58 .BR log1pf (),
  59 .BR log1pl ():
  60 .RS 4
  61 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  62     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  63     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  64 .RE
  65 .ad b
  66 .SH DESCRIPTION
  67 These functions return a value equivalent to
  68 .PP
  69 .nf
  70     log (1 + \fIx\fP)
  71 .fi
  72 .PP
  73 The result is computed in a way
  74 that is accurate even if the value of
  75 .I x
  76 is near zero.
  77 .SH RETURN VALUE
  78 On success, these functions return the natural logarithm of
  79 .IR "(1\ +\ x)" .
  80 .PP
  81 If
  82 .I x
  83 is a NaN,
  84 a NaN is returned.
  85 .PP
  86 If
  87 .I x
  88 is positive infinity, positive infinity is returned.
  89 .PP
  90 If
  91 .I x
  92 is \-1, a pole error occurs,
  93 and the functions return
  94 .RB - HUGE_VAL ,
  95 .RB - HUGE_VALF ,
  96 or
  97 .RB - HUGE_VALL ,
  98 respectively.
  99 .PP
 100 If
 101 .I x
 102 is less than \-1 (including negative infinity),
 103 a domain error occurs,
 104 and a NaN (not a number) is returned.
 105 .\" POSIX.1 specifies a possible range error if x is subnormal
 106 .\" glibc 2.8 doesn't do this
 107 .SH ERRORS
 108 See
 109 .BR math_error (7)
 110 for information on how to determine whether an error has occurred
 111 when calling these functions.
 112 .PP
 113 The following errors can occur:
 114 .TP
 115 Domain error: \fIx\fP is less than \-1
 116 .I errno
 117 is set to
 118 .BR EDOM
 119 (but see BUGS).
 120 An invalid floating-point exception
 121 .RB ( FE_INVALID )
 122 is raised.
 123 .TP
 124 Pole error: \fIx\fP is \-1
 125 .I errno
 126 is set to
 127 .BR ERANGE
 128 (but see BUGS).
 129 A divide-by-zero floating-point exception
 130 .RB ( FE_DIVBYZERO )
 131 is raised.
 132 .SH ATTRIBUTES
 133 For an explanation of the terms used in this section, see
 134 .BR attributes (7).
 135 .TS
 136 allbox;
 137 lbw27 lb lb
 138 l l l.
 139 Interface       Attribute       Value
 140 T{
 141 .BR log1p (),
 142 .BR log1pf (),
 143 .BR log1pl ()
 144 T}      Thread safety   MT-Safe
 145 .TE
 146 .SH CONFORMING TO
 147 C99, POSIX.1-2001, POSIX.1-2008.
 148 .\" BSD
 149 .SH BUGS
 150 Before version 2.22, the glibc implementation did not set
 151 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 152 .I errno
 153 to
 154 .B EDOM
 155 when a domain error occurred.
 156 .PP
 157 Before version 2.22, the glibc implementation did not set
 158 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 159 .I errno
 160 to
 161 .B ERANGE
 162 when a range error occurred.
 163 .SH SEE ALSO
 164 .BR exp (3),
 165 .BR expm1 (3),
 166 .BR log (3)