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>
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  26 .\"
  27 .\" Modified 2002-07-27 Walter Harms
  28 .\"     (walter.harms@informatik.uni-oldenburg.de)
  29 .\"
  30 .TH EXPM1 3  2017-09-15 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 expm1, expm1f, expm1l \- exponential minus 1
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <math.h>
  36 .PP
  37 .BI "double expm1(double " x );
  38 .BI "float expm1f(float " x );
  39 .BI "long double expm1l(long double " x );
  40 .PP
  41 .fi
  42 Link with \fI\-lm\fP.
  43 .PP
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .PP
  49 .ad l
  50 .BR expm1 ():
  51 .RS 4
  52 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  53     || _XOPEN_SOURCE\ >=\ 500
  54 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  55     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  56     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  57 .RE
  58 .br
  59 .BR expm1f (),
  60 .BR expm1l ():
  61 .RS 4
  62 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  63     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  64     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  65 .RE
  66 .ad b
  67 .SH DESCRIPTION
  68 These functions return a value equivalent to
  69 .PP
  70 .nf
  71     exp(x) \- 1
  72 .fi
  73 .PP
  74 The result is computed in a way that is accurate even if the value of
  75 .I x
  76 is near
  77 zero\(ema case where
  78 .I "exp(x) \- 1"
  79 would be inaccurate due to
  80 subtraction of two numbers that are nearly equal.
  81 .SH RETURN VALUE
  82 On success, these functions return
  83 .IR "exp(x)\ \-\ 1" .
  84 .PP
  85 If
  86 .I x
  87 is a NaN,
  88 a NaN is returned.
  89 .PP
  90 If
  91 .I x
  92 is +0 (\-0),
  93 +0 (\-0) is returned.
  94 .PP
  95 If
  96 .I x
  97 is positive infinity, positive infinity is returned.
  98 .PP
  99 If
 100 .I x
 101 is negative infinity, \-1 is returned.
 102 .PP
 103 If the result overflows, a range error occurs,
 104 and the functions return
 105 .RB - HUGE_VAL ,
 106 .RB - HUGE_VALF ,
 107 or
 108 .RB - HUGE_VALL ,
 109 respectively.
 110 .SH ERRORS
 111 See
 112 .BR math_error (7)
 113 for information on how to determine whether an error has occurred
 114 when calling these functions.
 115 .PP
 116 The following errors can occur:
 117 .TP
 118 Range error, overflow
 119 .I errno
 120 is set to
 121 .BR ERANGE
 122 (but see BUGS).
 123 An overflow floating-point exception
 124 .RB ( FE_OVERFLOW )
 125 is raised.
 126 .\"
 127 .\" POSIX.1 specifies an optional range error (underflow) if
 128 .\" x is subnormal.  Glibc does not implement this.
 129 .SH ATTRIBUTES
 130 For an explanation of the terms used in this section, see
 131 .BR attributes (7).
 132 .TS
 133 allbox;
 134 lbw27 lb lb
 135 l l l.
 136 Interface       Attribute       Value
 137 T{
 138 .BR expm1 (),
 139 .BR expm1f (),
 140 .BR expm1l ()
 141 T}      Thread safety   MT-Safe
 142 .TE
 143 .SH CONFORMING TO
 144 C99, POSIX.1-2001, POSIX.1-2008.
 145 .\" BSD.
 146 .SH BUGS
 147 Before glibc 2.17,
 148 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 149 on certain architectures (e.g., x86, but not x86_64)
 150 .BR expm1 ()
 151 raised a bogus underflow floating-point exception
 152 for some large negative
 153 .I x
 154 values (where the function result approaches \-1),
 155 .PP
 156 For some large positive
 157 .I x
 158 values,
 159 .BR expm1 ()
 160 raises a bogus invalid floating-point exception in addition to the expected
 161 overflow exception, and returns a NaN instead of positive infinity.
 162 .\" FIXME .
 163 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
 164 .\" e.g., expm1(1e5) through expm1(1.00199970127e5),
 165 .\" but not expm1(1.00199970128e5) and beyond.
 166 .PP
 167 Before version 2.11,
 168 .\" It looks like the fix was in 2.11, or possibly 2.12.
 169 .\" I have no test system for 2.11, but 2.12 passes.
 170 .\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
 171 .\" like the changes were in 2.11.
 172 the glibc implementation did not set
 173 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
 174 .I errno
 175 to
 176 .B ERANGE
 177 when a range error occurred.
 178 .SH SEE ALSO
 179 .BR exp (3),
 180 .BR log (3),
 181 .BR log1p (3)