man3/log1p.3

   1 .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .\" Modified 2002-07-27 by Walter Harms
   8 .\"     (walter.harms@informatik.uni-oldenburg.de)
   9 .TH LOG1P 3 2021-03-22 GNU "Linux Programmer's Manual"
  10 .SH NAME
  11 log1p, log1pf, log1pl \-  logarithm of 1 plus argument
  12 .SH LIBRARY
  13 Math library
  14 .RI ( libm ", " \-lm )
  15 .SH SYNOPSIS
  16 .nf
  17 .B #include <math.h>
  18 .PP
  19 .BI "double log1p(double " x );
  20 .BI "float log1pf(float " x );
  21 .BI "long double log1pl(long double " x );
  22 .PP
  23 .fi
  24 .RS -4
  25 Feature Test Macro Requirements for glibc (see
  26 .BR feature_test_macros (7)):
  27 .RE
  28 .PP
  29 .nf
  30 .BR log1p ():
  31     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  32         || _XOPEN_SOURCE >= 500
  33 .\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  34         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  35         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  36 .fi
  37 .PP
  38 .BR log1pf (),
  39 .BR log1pl ():
  40 .nf
  41     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  42         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  43         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  44 .fi
  45 .SH DESCRIPTION
  46 These functions return a value equivalent to
  47 .PP
  48 .nf
  49     log (1 + \fIx\fP)
  50 .fi
  51 .PP
  52 The result is computed in a way
  53 that is accurate even if the value of
  54 .I x
  55 is near zero.
  56 .SH RETURN VALUE
  57 On success, these functions return the natural logarithm of
  58 .IR "(1\ +\ x)" .
  59 .PP
  60 If
  61 .I x
  62 is a NaN,
  63 a NaN is returned.
  64 .PP
  65 If
  66 .I x
  67 is positive infinity, positive infinity is returned.
  68 .PP
  69 If
  70 .I x
  71 is \-1, a pole error occurs,
  72 and the functions return
  73 .RB \- HUGE_VAL ,
  74 .RB \- HUGE_VALF ,
  75 or
  76 .RB \- HUGE_VALL ,
  77 respectively.
  78 .PP
  79 If
  80 .I x
  81 is less than \-1 (including negative infinity),
  82 a domain error occurs,
  83 and a NaN (not a number) is returned.
  84 .\" POSIX.1 specifies a possible range error if x is subnormal
  85 .\" glibc 2.8 doesn't do this
  86 .SH ERRORS
  87 See
  88 .BR math_error (7)
  89 for information on how to determine whether an error has occurred
  90 when calling these functions.
  91 .PP
  92 The following errors can occur:
  93 .TP
  94 Domain error: \fIx\fP is less than \-1
  95 .I errno
  96 is set to
  97 .B EDOM
  98 (but see BUGS).
  99 An invalid floating-point exception
 100 .RB ( FE_INVALID )
 101 is raised.
 102 .TP
 103 Pole error: \fIx\fP is \-1
 104 .I errno
 105 is set to
 106 .B ERANGE
 107 (but see BUGS).
 108 A divide-by-zero floating-point exception
 109 .RB ( FE_DIVBYZERO )
 110 is raised.
 111 .SH ATTRIBUTES
 112 For an explanation of the terms used in this section, see
 113 .BR attributes (7).
 114 .ad l
 115 .nh
 116 .TS
 117 allbox;
 118 lbx lb lb
 119 l l l.
 120 Interface       Attribute       Value
 121 T{
 122 .BR log1p (),
 123 .BR log1pf (),
 124 .BR log1pl ()
 125 T}      Thread safety   MT-Safe
 126 .TE
 127 .hy
 128 .ad
 129 .sp 1
 130 .SH CONFORMING TO
 131 C99, POSIX.1-2001, POSIX.1-2008.
 132 .\" BSD
 133 .SH BUGS
 134 Before version 2.22, the glibc implementation did not set
 135 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 136 .I errno
 137 to
 138 .B EDOM
 139 when a domain error occurred.
 140 .PP
 141 Before version 2.22, the glibc implementation did not set
 142 .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792
 143 .I errno
 144 to
 145 .B ERANGE
 146 when a range error occurred.
 147 .SH SEE ALSO
 148 .BR exp (3),
 149 .BR expm1 (3),
 150 .BR log (3)