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  2015-04-19 "" "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 .sp
  37 .BI "double expm1(double " x );
  38 .br
  39 .BI "float expm1f(float " x );
  40 .br
  41 .BI "long double expm1l(long double " x );
  42 .sp
  43 .fi
  44 Link with \fI\-lm\fP.
  45 .sp
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .in
  50 .sp
  51 .ad l
  52 .BR expm1 ():
  53 .RS 4
  54 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  55     || _XOPEN_SOURCE\ >=\ 500
  56 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  57     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  58     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  59 .RE
  60 .br
  61 .BR expm1f (),
  62 .BR expm1l ():
  63 .RS 4
  64 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  65     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  66     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  67 .RE
  68 .ad b
  69 .SH DESCRIPTION
  70 These functions return a value equivalent to
  71 .nf
  72
  73     exp(x) \- 1
  74
  75 .fi
  76 The result is computed in a way that is accurate even if the value of
  77 .I x
  78 is near
  79 zero\(ema case where
  80 .I "exp(x) \- 1"
  81 would be inaccurate due to
  82 subtraction of two numbers that are nearly equal.
  83 .SH RETURN VALUE
  84 On success, these functions return
  85 .IR "exp(x)\ \-\ 1" .
  86
  87 If
  88 .I x
  89 is a NaN,
  90 a NaN is returned.
  91
  92 If
  93 .I x
  94 is +0 (\-0),
  95 +0 (\-0) is returned.
  96
  97 If
  98 .I x
  99 is positive infinity, positive infinity is returned.
 100
 101 If
 102 .I x
 103 is negative infinity, \-1 is returned.
 104
 105 If the result overflows, a range error occurs,
 106 and the functions return
 107 .RB - HUGE_VAL ,
 108 .RB - HUGE_VALF ,
 109 or
 110 .RB - HUGE_VALL ,
 111 respectively.
 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 Range error, overflow
 121 .I errno
 122 is set to
 123 .BR ERANGE
 124 (but see BUGS).
 125 An overflow floating-point exception
 126 .RB ( FE_OVERFLOW )
 127 is raised.
 128 .\"
 129 .\" POSIX.1 specifies an optional range error (underflow) if
 130 .\" x is subnormal.  Glibc does not implement this.
 131 .SH ATTRIBUTES
 132 For an explanation of the terms used in this section, see
 133 .BR attributes (7).
 134 .TS
 135 allbox;
 136 lbw27 lb lb
 137 l l l.
 138 Interface       Attribute       Value
 139 T{
 140 .BR expm1 (),
 141 .BR expm1f (),
 142 .BR expm1l ()
 143 T}      Thread safety   MT-Safe
 144 .TE
 145 .SH CONFORMING TO
 146 C99, POSIX.1-2001, POSIX.1-2008.
 147 .\" BSD.
 148 .SH BUGS
 149 For some large negative
 150 .I x
 151 values (where the function result approaches \-1),
 152 .BR expm1 ()
 153 raises a bogus underflow floating-point exception.
 154 .\" FIXME .
 155 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 156
 157 For some large positive
 158 .I x
 159 values,
 160 .BR expm1 ()
 161 raises a bogus invalid floating-point exception in addition to the expected
 162 overflow exception, and returns a NaN instead of positive infinity.
 163 .\" FIXME .
 164 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
 165 .\" e.g., expm1(1e5) through expm1(1.00199970127e5),
 166 .\" but not expm1(1.00199970128e5) and beyond.
 167
 168 Before version 2.11,
 169 .\" It looks like the fix was in 2.11, or possibly 2.12.
 170 .\" I have no test system for 2.11, but 2.12 passes.
 171 .\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
 172 .\" like the changes were in 2.11.
 173 the glibc implementation did not set
 174 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
 175 .I errno
 176 to
 177 .B ERANGE
 178 when a range error occurred.
 179 .SH SEE ALSO
 180 .BR exp (3),
 181 .BR log (3),
 182 .BR log1p (3)