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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
  55 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
  56 _POSIX_C_SOURCE\ >=\ 200112L;
  57 .br
  58 or
  59 .I cc\ -std=c99
  60 .RE
  61 .br
  62 .BR expm1f (),
  63 .BR expm1l ():
  64 .RS 4
  65 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
  66 _POSIX_C_SOURCE\ >=\ 200112L;
  67 .br
  68 or
  69 .I cc\ -std=c99
  70 .RE
  71 .ad b
  72 .SH DESCRIPTION
  73 These functions return a value equivalent to
  74 .nf
  75
  76     exp(x) \- 1
  77
  78 .fi
  79 The result is computed in a way that is accurate even if the value of
  80 .I x
  81 is near
  82 zero\(ema case where
  83 .I "exp(x) \- 1"
  84 would be inaccurate due to
  85 subtraction of two numbers that are nearly equal.
  86 .SH RETURN VALUE
  87 On success, these functions return
  88 .IR "exp(x)\ \-\ 1" .
  89
  90 If
  91 .I x
  92 is a NaN,
  93 a NaN is returned.
  94
  95 If
  96 .I x
  97 is +0 (\-0),
  98 +0 (\-0) is returned.
  99
 100 If
 101 .I x
 102 is positive infinity, positive infinity is returned.
 103
 104 If
 105 .I x
 106 is negative infinity, \-1 is returned.
 107
 108 If the result overflows, a range error occurs,
 109 and the functions return
 110 .RB - HUGE_VAL ,
 111 .RB - HUGE_VALF ,
 112 or
 113 .RB - HUGE_VALL ,
 114 respectively.
 115 .SH ERRORS
 116 See
 117 .BR math_error (7)
 118 for information on how to determine whether an error has occurred
 119 when calling these functions.
 120 .PP
 121 The following errors can occur:
 122 .TP
 123 Range error, overflow
 124 .I errno
 125 is set to
 126 .BR ERANGE
 127 (but see BUGS).
 128 An overflow floating-point exception
 129 .RB ( FE_OVERFLOW )
 130 is raised.
 131 .\"
 132 .\" POSIX.1 specifies an optional range error (underflow) if
 133 .\" x is subnormal.  Glibc does not implement this.
 134 .SH ATTRIBUTES
 135 For an explanation of the terms used in this section, see
 136 .BR attributes (7).
 137 .TS
 138 allbox;
 139 lbw27 lb lb
 140 l l l.
 141 Interface       Attribute       Value
 142 T{
 143 .BR expm1 (),
 144 .BR expm1f (),
 145 .BR expm1l ()
 146 T}      Thread safety   MT-Safe
 147 .TE
 148 .SH CONFORMING TO
 149 C99, POSIX.1-2001, POSIX.1-2008.
 150 .\" BSD.
 151 .SH BUGS
 152 For some large negative
 153 .I x
 154 values (where the function result approaches \-1),
 155 .BR expm1 ()
 156 raises a bogus underflow floating-point exception.
 157 .\" FIXME .
 158 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 159
 160 For some large positive
 161 .I x
 162 values,
 163 .BR expm1 ()
 164 raises a bogus invalid floating-point exception in addition to the expected
 165 overflow exception, and returns a NaN instead of positive infinity.
 166 .\" FIXME .
 167 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
 168 .\" e.g., expm1(1e5) through expm1(1.00199970127e5),
 169 .\" but not expm1(1.00199970128e5) and beyond.
 170
 171 Before version 2.11,
 172 .\" It looks like the fix was in 2.11, or possibly 2.12.
 173 .\" I have no test system for 2.11, but 2.12 passes.
 174 .\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
 175 .\" like the changes were in 2.11.
 176 the glibc implementation did not set
 177 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
 178 .I errno
 179 to
 180 .B ERANGE
 181 when a range error occurred.
 182 .SH SEE ALSO
 183 .BR exp (3),
 184 .BR log (3),
 185 .BR log1p (3)