man3/expm1.3

   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 Walter Harms
   8 .\"     (walter.harms@informatik.uni-oldenburg.de)
   9 .\"
  10 .TH EXPM1 3 2021-03-22 GNU "Linux Programmer's Manual"
  11 .SH NAME
  12 expm1, expm1f, expm1l \- exponential minus 1
  13 .SH LIBRARY
  14 Math library
  15 .RI ( libm ", " \-lm )
  16 .SH SYNOPSIS
  17 .nf
  18 .B #include <math.h>
  19 .PP
  20 .BI "double expm1(double " x );
  21 .BI "float expm1f(float " x );
  22 .BI "long double expm1l(long double " x );
  23 .PP
  24 .fi
  25 .RS -4
  26 Feature Test Macro Requirements for glibc (see
  27 .BR feature_test_macros (7)):
  28 .RE
  29 .PP
  30 .BR expm1 ():
  31 .nf
  32     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  33         || _XOPEN_SOURCE >= 500
  34 .\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  35         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  36         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  37 .fi
  38 .PP
  39 .BR expm1f (),
  40 .BR expm1l ():
  41 .nf
  42     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  43         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  44         || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  45 .fi
  46 .SH DESCRIPTION
  47 These functions return a value equivalent to
  48 .PP
  49 .nf
  50     exp(x) \- 1
  51 .fi
  52 .PP
  53 The result is computed in a way that is accurate even if the value of
  54 .I x
  55 is near
  56 zero\(ema case where
  57 .I "exp(x) \- 1"
  58 would be inaccurate due to
  59 subtraction of two numbers that are nearly equal.
  60 .SH RETURN VALUE
  61 On success, these functions return
  62 .IR "exp(x)\ \-\ 1" .
  63 .PP
  64 If
  65 .I x
  66 is a NaN,
  67 a NaN is returned.
  68 .PP
  69 If
  70 .I x
  71 is +0 (\-0),
  72 +0 (\-0) is returned.
  73 .PP
  74 If
  75 .I x
  76 is positive infinity, positive infinity is returned.
  77 .PP
  78 If
  79 .I x
  80 is negative infinity, \-1 is returned.
  81 .PP
  82 If the result overflows, a range error occurs,
  83 and the functions return
  84 .RB \- HUGE_VAL ,
  85 .RB \- HUGE_VALF ,
  86 or
  87 .RB \- HUGE_VALL ,
  88 respectively.
  89 .SH ERRORS
  90 See
  91 .BR math_error (7)
  92 for information on how to determine whether an error has occurred
  93 when calling these functions.
  94 .PP
  95 The following errors can occur:
  96 .TP
  97 Range error, overflow
  98 .I errno
  99 is set to
 100 .B ERANGE
 101 (but see BUGS).
 102 An overflow floating-point exception
 103 .RB ( FE_OVERFLOW )
 104 is raised.
 105 .\"
 106 .\" POSIX.1 specifies an optional range error (underflow) if
 107 .\" x is subnormal.  Glibc does not implement this.
 108 .SH ATTRIBUTES
 109 For an explanation of the terms used in this section, see
 110 .BR attributes (7).
 111 .ad l
 112 .nh
 113 .TS
 114 allbox;
 115 lbx lb lb
 116 l l l.
 117 Interface       Attribute       Value
 118 T{
 119 .BR expm1 (),
 120 .BR expm1f (),
 121 .BR expm1l ()
 122 T}      Thread safety   MT-Safe
 123 .TE
 124 .hy
 125 .ad
 126 .sp 1
 127 .SH CONFORMING TO
 128 C99, POSIX.1-2001, POSIX.1-2008.
 129 .\" BSD.
 130 .SH BUGS
 131 Before glibc 2.17,
 132 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 133 on certain architectures (e.g., x86, but not x86_64)
 134 .BR expm1 ()
 135 raised a bogus underflow floating-point exception
 136 for some large negative
 137 .I x
 138 values (where the function result approaches \-1).
 139 .PP
 140 Before approximately glibc version 2.11,
 141 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
 142 .\" e.g., expm1(1e5) through expm1(1.00199970127e5),
 143 .\" but not expm1(1.00199970128e5) and beyond.
 144 .BR expm1 ()
 145 raised a bogus invalid floating-point exception in addition to the expected
 146 overflow exception, and returned a NaN instead of positive infinity,
 147 for some large positive
 148 .I x
 149 values.
 150 .PP
 151 Before version 2.11,
 152 .\" It looks like the fix was in 2.11, or possibly 2.12.
 153 .\" I have no test system for 2.11, but 2.12 passes.
 154 .\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
 155 .\" like the changes were in 2.11.
 156 the glibc implementation did not set
 157 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
 158 .I errno
 159 to
 160 .B ERANGE
 161 when a range error occurred.
 162 .SH SEE ALSO
 163 .BR exp (3),
 164 .BR log (3),
 165 .BR log1p (3)