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 .\" Permission is granted to make and distribute verbatim copies of this
   6 .\" manual provided the copyright notice and this permission notice are
   7 .\" preserved on all copies.
   8 .\"
   9 .\" Permission is granted to copy and distribute modified versions of this
  10 .\" manual under the conditions for verbatim copying, provided that the
  11 .\" entire resulting derived work is distributed under the terms of a
  12 .\" permission notice identical to this one.
  13 .\"
  14 .\" Since the Linux kernel and libraries are constantly changing, this
  15 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  16 .\" responsibility for errors or omissions, or for damages resulting from
  17 .\" the use of the information contained herein.  The author(s) may not
  18 .\" have taken the same level of care in the production of this manual,
  19 .\" which is licensed free of charge, as they might when working
  20 .\" professionally.
  21 .\"
  22 .\" Formatted or processed versions of this manual, if unaccompanied by
  23 .\" the source, must acknowledge the copyright and authors of this work.
  24 .\"
  25 .\" Modified 2002-07-27 Walter Harms
  26 .\"     (walter.harms@informatik.uni-oldenburg.de)
  27 .\"
  28 .TH EXPM1 3  2010-09-12 "" "Linux Programmer's Manual"
  29 .SH NAME
  30 expm1, expm1f, expm1l \- exponential minus 1
  31 .SH SYNOPSIS
  32 .nf
  33 .B #include <math.h>
  34 .sp
  35 .BI "double expm1(double " x );
  36 .br
  37 .BI "float expm1f(float " x );
  38 .br
  39 .BI "long double expm1l(long double " x );
  40 .sp
  41 .fi
  42 Link with \fI\-lm\fP.
  43 .sp
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .sp
  49 .ad l
  50 .BR expm1 ():
  51 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
  52 .I cc\ -std=c99
  53 .br
  54 .BR expm1f (),
  55 .BR expm1l ():
  56 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
  57 .I cc\ -std=c99
  58 .ad b
  59 .SH DESCRIPTION
  60 .I expm1(x)
  61 returns a value equivalent to
  62 .nf
  63
  64     exp(x) \- 1
  65
  66 .fi
  67 It is
  68 computed in a way that is accurate even if the value of \fIx\fP is near
  69 zero\(ema case where
  70 .I "exp(x) \- 1"
  71 would be inaccurate due to
  72 subtraction of two numbers that are nearly equal.
  73 .SH RETURN VALUE
  74 On success, these functions return
  75 .IR "exp(x)\ \-\ 1" .
  76
  77 If
  78 .I x
  79 is a NaN,
  80 a NaN is returned.
  81
  82 If
  83 .I x
  84 is +0 (\-0),
  85 +0 (\-0) is returned.
  86
  87 If
  88 .I x
  89 is positive infinity, positive infinity is returned.
  90
  91 If
  92 .I x
  93 is negative infinity, \-1 is returned.
  94
  95 If the result overflows, a range error occurs,
  96 and the functions return
  97 .RB - HUGE_VAL ,
  98 .RB - HUGE_VALF ,
  99 or
 100 .RB - HUGE_VALL ,
 101 respectively.
 102 .SH ERRORS
 103 See
 104 .BR math_error (7)
 105 for information on how to determine whether an error has occurred
 106 when calling these functions.
 107 .PP
 108 The following errors can occur:
 109 .TP
 110 Range error, overflow
 111 .I errno
 112 is set to
 113 .BR ERANGE
 114 (but see BUGS).
 115 An overflow floating-point exception
 116 .RB ( FE_OVERFLOW )
 117 is raised.
 118 .\"
 119 .\" POSIX.1 specifies an optional range error (underflow) if
 120 .\" x is subnormal.  Glibc does not implement this.
 121 .SH "CONFORMING TO"
 122 C99, POSIX.1-2001.
 123 .\" BSD.
 124 .SH BUGS
 125 For some large negative
 126 .I x
 127 values (where the function result approaches \-1),
 128 .BR expm1 ()
 129 raises a bogus underflow floating-point exception.
 130 .\" FIXME .
 131 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 132
 133 For some large positive
 134 .I x
 135 values,
 136 .BR expm1 ()
 137 raises a bogus invalid floating-point exception in addition to the expected
 138 overflow exception, and returns a NaN instead of positive infinity.
 139 .\" FIXME .
 140 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
 141 .\" e.g., expm1(1e5) through expm1(1.00199970127e5),
 142 .\" but not expm1(1.00199970128e5) and beyond.
 143 .SH BUGS
 144 Before version 2.11,
 145 .\" It looks like the fix was in 2.11, or possibly 2.12.
 146 .\" I have no test system for 2.11, but 2.12 passes.
 147 .\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
 148 .\" like the changes were in 2.11.
 149 the glibc implementation did not set
 150 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
 151 .I errno
 152 to
 153 .B ERANGE
 154 when a range error occurred.
 155 .SH "SEE ALSO"
 156 .BR exp (3),
 157 .BR log (3),
 158 .BR log1p (3)