.\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\" <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
-.\"
+.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
-.\"
+.\"
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+.\" %%%LICENSE_END
.\"
.\" Modified 2002-07-27 Walter Harms
.\" (walter.harms@informatik.uni-oldenburg.de)
.\"
-.TH EXPM1 3 2002-07-27 "" "Linux Programmer's Manual"
+.TH EXPM1 3 2017-09-15 "" "Linux Programmer's Manual"
.SH NAME
-expm1, expm1f, expm1l \- exponential minus 1
+expm1, expm1f, expm1l \- exponential minus 1
.SH SYNOPSIS
.nf
.B #include <math.h>
-.sp
+.PP
.BI "double expm1(double " x );
-.br
.BI "float expm1f(float " x );
-.br
.BI "long double expm1l(long double " x );
-.sp
+.PP
.fi
-Link with \-lm.
+Link with \fI\-lm\fP.
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.PP
+.ad l
+.BR expm1 ():
+.RS 4
+_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
+ || _XOPEN_SOURCE\ >=\ 500
+.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+ || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.RE
+.br
+.BR expm1f (),
+.BR expm1l ():
+.RS 4
+_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
+ || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.RE
+.ad b
.SH DESCRIPTION
-.BI expm1( x )
-returns a value equivalent to `exp (\fIx\fP) \- 1'. It is
-computed in a way that is accurate even if the value of \fIx\fP is near
-zero--a case where `exp (\fIx\fP) \- 1' would be inaccurate due to
+These functions return a value equivalent to
+.PP
+.nf
+ exp(x) \- 1
+.fi
+.PP
+The result is computed in a way that is accurate even if the value of
+.I x
+is near
+zero\(ema case where
+.I "exp(x) \- 1"
+would be inaccurate due to
subtraction of two numbers that are nearly equal.
-.SH "CONFORMING TO"
-BSD, C99.
-The float and the long double variants are C99 requirements.
-.SH "SEE ALSO"
+.SH RETURN VALUE
+On success, these functions return
+.IR "exp(x)\ \-\ 1" .
+.PP
+If
+.I x
+is a NaN,
+a NaN is returned.
+.PP
+If
+.I x
+is +0 (\-0),
++0 (\-0) is returned.
+.PP
+If
+.I x
+is positive infinity, positive infinity is returned.
+.PP
+If
+.I x
+is negative infinity, \-1 is returned.
+.PP
+If the result overflows, a range error occurs,
+and the functions return
+.RB - HUGE_VAL ,
+.RB - HUGE_VALF ,
+or
+.RB - HUGE_VALL ,
+respectively.
+.SH ERRORS
+See
+.BR math_error (7)
+for information on how to determine whether an error has occurred
+when calling these functions.
+.PP
+The following errors can occur:
+.TP
+Range error, overflow
+.I errno
+is set to
+.BR ERANGE
+(but see BUGS).
+An overflow floating-point exception
+.RB ( FE_OVERFLOW )
+is raised.
+.\"
+.\" POSIX.1 specifies an optional range error (underflow) if
+.\" x is subnormal. Glibc does not implement this.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbw27 lb lb
+l l l.
+Interface Attribute Value
+T{
+.BR expm1 (),
+.BR expm1f (),
+.BR expm1l ()
+T} Thread safety MT-Safe
+.TE
+.SH CONFORMING TO
+C99, POSIX.1-2001, POSIX.1-2008.
+.\" BSD.
+.SH BUGS
+Before glibc 2.17,
+.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
+on certain architectures (e.g., x86, but not x86_64)
+.BR expm1 ()
+raised a bogus underflow floating-point exception
+for some large negative
+.I x
+values (where the function result approaches \-1),
+.PP
+Before approximately glibc version 2.11,
+.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
+.\" e.g., expm1(1e5) through expm1(1.00199970127e5),
+.\" but not expm1(1.00199970128e5) and beyond.
+.BR expm1 ()
+raised a bogus invalid floating-point exception in addition to the expected
+overflow exception, and returned a NaN instead of positive infinity.
+for some large positive
+.I x
+values,
+.PP
+Before version 2.11,
+.\" It looks like the fix was in 2.11, or possibly 2.12.
+.\" I have no test system for 2.11, but 2.12 passes.
+.\" From the source (sysdeps/i386/fpu/s_expm1.S) it looks
+.\" like the changes were in 2.11.
+the glibc implementation did not set
+.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
+.I errno
+to
+.B ERANGE
+when a range error occurred.
+.SH SEE ALSO
.BR exp (3),
.BR log (3),
.BR log1p (3)
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