mirror of https://github.com/mkerrisk/man-pages
152 lines
3.9 KiB
Groff
152 lines
3.9 KiB
Groff
.\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com>
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.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified 2002-07-27 Walter Harms
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.\" (walter.harms@informatik.uni-oldenburg.de)
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.\"
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.TH EXPM1 3 2008-08-05 "" "Linux Programmer's Manual"
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.SH NAME
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expm1, expm1f, expm1l \- exponential minus 1
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.SH SYNOPSIS
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.nf
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.B #include <math.h>
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.sp
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.BI "double expm1(double " x );
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.br
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.BI "float expm1f(float " x );
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.br
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.BI "long double expm1l(long double " x );
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.sp
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.fi
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Link with \fI\-lm\fP.
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR expm1 ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.br
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.BR expm1f (),
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.BR expm1l ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.ad b
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.SH DESCRIPTION
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.I expm1(x)
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returns a value equivalent to
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.nf
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exp(x) \- 1
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.fi
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It is
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computed in a way that is accurate even if the value of \fIx\fP is near
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zero\(ema case where
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.I "exp(x) \- 1"
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would be inaccurate due to
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subtraction of two numbers that are nearly equal.
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.SH RETURN VALUE
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On success, these functions return
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.IR "exp(x)\ \-\ 1" .
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If
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.I x
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is a NaN,
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a NaN is returned.
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If
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.I x
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is +0 (\-0),
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+0 (\-0) is returned.
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If
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.I x
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is positive infinity, positive infinity is returned.
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If
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.I x
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is negative infinity, \-1 is returned.
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If the result overflows, a range error occurs,
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and the functions return
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.RB - HUGE_VAL ,
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.RB - HUGE_VALF ,
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or
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.RB - HUGE_VALL ,
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respectively.
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.SH ERRORS
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See
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.BR math_error (7)
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for information on how to determine whether an error has occurred
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when calling these functions.
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.PP
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The following errors can occur:
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.TP
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Range error, overflow
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.\" .I errno
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.\" is set to
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.\" .BR ERANGE .
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An overflow floating-point exception
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.RB ( FE_OVERFLOW )
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is raised.
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.PP
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These functions do not set
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.IR errno .
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.\" FIXME . Is it intentional that these functions do not set errno?
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.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6788
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.\"
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.\"
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.\" POSIX.1 specifies an optional range error (underflow) if
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.\" x is subnormal. Glibc does not implement this.
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.SH "CONFORMING TO"
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C99, POSIX.1-2001.
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.\" BSD.
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.SH BUGS
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For some large negative
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.I x
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values (where the function result approaches \-1),
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.BR expm1 ()
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raises a bogus underflow floating-point exception.
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.\" FIXME .
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.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
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For some large positive
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.I x
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values,
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.BR expm1 ()
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raises a bogus invalid floating-point exception in addition to the expected
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overflow exception, and returns a NaN instead of positive infinity.
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.\" FIXME .
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.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6814
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.\" e.g., expm1(1e5) through expm1(1.00199970127e5),
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.\" but not expm1(1.00199970128e5) and beyond.
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.SH "SEE ALSO"
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.BR exp (3),
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.BR log (3),
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.BR log1p (3)
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