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   2015-04-19 "" "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 .sp
  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 .sp
  42 .fi
  43 Link with \fI\-lm\fP.
  44 .sp
  45 .in -4n
  46 Feature Test Macro Requirements for glibc (see
  47 .BR feature_test_macros (7)):
  48 .in
  49 .sp
  50 .ad l
  51 .BR log1p ():
  52 .RS 4
  53 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  54 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
  55 _POSIX_C_SOURCE\ >=\ 200112L;
  56 .br
  57 or
  58 .I cc\ -std=c99
  59 .RE
  60 .br
  61 .BR log1pf (),
  62 .BR log1pl ():
  63 .RS 4
  64 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  65 _POSIX_C_SOURCE\ >=\ 200112L;
  66 .br
  67 or
  68 .I cc\ -std=c99
  69 .RE
  70 .ad b
  71 .SH DESCRIPTION
  72 These functions return a value equivalent to
  73 .nf
  74
  75     log (1 + \fIx\fP)
  76
  77 .fi
  78 The result is computed in a way
  79 that is accurate even if the value of
  80 .I x
  81 is near zero.
  82 .SH RETURN VALUE
  83 On success, these functions return the natural logarithm of
  84 .IR "(1\ +\ x)" .
  85
  86 If
  87 .I x
  88 is a NaN,
  89 a NaN is returned.
  90
  91 If
  92 .I x
  93 is positive infinity, positive infinity is returned.
  94
  95 If
  96 .I x
  97 is \-1, a pole error occurs,
  98 and the functions return
  99 .RB - HUGE_VAL ,
 100 .RB - HUGE_VALF ,
 101 or
 102 .RB - HUGE_VALL ,
 103 respectively.
 104
 105 If
 106 .I x
 107 is less than \-1 (including negative infinity),
 108 a domain error occurs,
 109 and a NaN (not a number) is returned.
 110 .\" POSIX.1 specifies a possible range error if x is subnormal
 111 .\" glibc 2.8 doesn't do this
 112 .SH ERRORS
 113 See
 114 .BR math_error (7)
 115 for information on how to determine whether an error has occurred
 116 when calling these functions.
 117 .PP
 118 The following errors can occur:
 119 .TP
 120 Domain error: \fIx\fP is less than \-1
 121 .\" .I errno
 122 .\" is set to
 123 .\" .BR EDOM .
 124 An invalid floating-point exception
 125 .RB ( FE_INVALID )
 126 is raised.
 127 .TP
 128 Pole error: \fIx\fP is \-1
 129 .\" .I errno
 130 .\" is set to
 131 .\" .BR ERANGE .
 132 A divide-by-zero floating-point exception
 133 .RB ( FE_DIVBYZERO )
 134 is raised.
 135 .PP
 136 These functions do not set
 137 .IR errno .
 138 .\" FIXME . Is it intentional that these functions do not set errno?
 139 .\" log(), log2(), log10() do set errno
 140 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6792
 141 .SH ATTRIBUTES
 142 For an explanation of the terms used in this section, see
 143 .BR attributes (7).
 144 .TS
 145 allbox;
 146 lbw27 lb lb
 147 l l l.
 148 Interface       Attribute       Value
 149 T{
 150 .BR log1p (),
 151 .BR log1pf (),
 152 .BR log1pl ()
 153 T}      Thread safety   MT-Safe
 154 .TE
 155 .SH CONFORMING TO
 156 C99, POSIX.1-2001, POSIX.1-2008.
 157 .\" BSD
 158 .SH SEE ALSO
 159 .BR exp (3),
 160 .BR expm1 (3),
 161 .BR log (3)