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   2016-03-15 "" "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 .br
  38 .BI "float log1pf(float " x );
  39 .br
  40 .BI "long double log1pl(long double " x );
  41 .PP
  42 .fi
  43 Link with \fI\-lm\fP.
  44 .PP
  45 .in -4n
  46 Feature Test Macro Requirements for glibc (see
  47 .BR feature_test_macros (7)):
  48 .in
  49 .PP
  50 .ad l
  51 .BR log1p ():
  52 .RS 4
  53 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  54     || _XOPEN_SOURCE\ >=\ 500
  55 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  56     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  57     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  58 .RE
  59 .br
  60 .BR log1pf (),
  61 .BR log1pl ():
  62 .RS 4
  63 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  64     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  65     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  66 .RE
  67 .ad b
  68 .SH DESCRIPTION
  69 These functions return a value equivalent to
  70 .PP
  71 .nf
  72     log (1 + \fIx\fP)
  73 .fi
  74 .PP
  75 The result is computed in a way
  76 that is accurate even if the value of
  77 .I x
  78 is near zero.
  79 .SH RETURN VALUE
  80 On success, these functions return the natural logarithm of
  81 .IR "(1\ +\ x)" .
  82 .PP
  83 If
  84 .I x
  85 is a NaN,
  86 a NaN is returned.
  87 .PP
  88 If
  89 .I x
  90 is positive infinity, positive infinity is returned.
  91 .PP
  92 If
  93 .I x
  94 is \-1, a pole error occurs,
  95 and the functions return
  96 .RB - HUGE_VAL ,
  97 .RB - HUGE_VALF ,
  98 or
  99 .RB - HUGE_VALL ,
 100 respectively.
 101 .PP
 102 If
 103 .I x
 104 is less than \-1 (including negative infinity),
 105 a domain error occurs,
 106 and a NaN (not a number) is returned.
 107 .\" POSIX.1 specifies a possible range error if x is subnormal
 108 .\" glibc 2.8 doesn't do this
 109 .SH ERRORS
 110 See
 111 .BR math_error (7)
 112 for information on how to determine whether an error has occurred
 113 when calling these functions.
 114 .PP
 115 The following errors can occur:
 116 .TP
 117 Domain error: \fIx\fP is less than \-1
 118 .I errno
 119 is set to
 120 .BR EDOM
 121 (but see BUGS).
 122 An invalid floating-point exception
 123 .RB ( FE_INVALID )
 124 is raised.
 125 .TP
 126 Pole error: \fIx\fP is \-1
 127 .I errno
 128 is set to
 129 .BR ERANGE
 130 (but see BUGS).
 131 A divide-by-zero floating-point exception
 132 .RB ( FE_DIVBYZERO )
 133 is raised.
 134 .SH ATTRIBUTES
 135 For an explanation of the terms used in this section, see
 136 .BR attributes (7).
 137 .TS
 138 allbox;
 139 lbw27 lb lb
 140 l l l.
 141 Interface       Attribute       Value
 142 T{
 143 .BR log1p (),
 144 .BR log1pf (),
 145 .BR log1pl ()
 146 T}      Thread safety   MT-Safe
 147 .TE
 148 .SH CONFORMING TO
 149 C99, POSIX.1-2001, POSIX.1-2008.
 150 .\" BSD
 151 .SH BUGS
 152 Before version 2.22, the glibc implementation did not set
 153 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 154 .I errno
 155 to
 156 .B EDOM
 157 when a domain error occurred.
 158 .PP
 159 Before version 2.22, the glibc implementation did not set
 160 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 161 .I errno
 162 to
 163 .B ERANGE
 164 when a range error occurred.
 165 .SH SEE ALSO
 166 .BR exp (3),
 167 .BR expm1 (3),
 168 .BR log (3)