226 lines
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226 lines
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HTML
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>signal</title>
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<basefont size="3"> <a name="signal"></a> <a name="tag_03_690"></a><!-- signal -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_690_01"></a>NAME</h4>
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<blockquote>signal - signal management</blockquote>
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<h4><a name="tag_03_690_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/signal.h.html">signal.h</a>><br>
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<br>
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void (*signal(int</tt> <i>sig</i><tt>, void (*</tt><i>func</i><tt>)(int)))(int);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_690_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Use
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of this function is unspecified in a multi-threaded process. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>The <i>signal</i>() function chooses one of three ways in which receipt of the signal number <i>sig</i> is to be subsequently
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handled. If the value of <i>func</i> is SIG_DFL, default handling for that signal shall occur. If the value of <i>func</i> is
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SIG_IGN, the signal shall be ignored. Otherwise, the application shall ensure that <i>func</i> points to a function to be called
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when that signal occurs. An invocation of such a function because of a signal, or (recursively) of any further functions called by
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that invocation (other than functions in the standard library), is called a "signal handler".</p>
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<p>When a signal occurs, and <i>func</i> points to a function, it is implementation-defined whether the equivalent of a:</p>
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<pre>
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<tt>signal(</tt><i>sig</i><tt>, SIG_DFL);
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</tt>
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</pre>
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<p>is executed or the implementation prevents some implementation-defined set of signals (at least including <i>sig</i>) from
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occurring until the current signal handling has completed. (If the value of <i>sig</i> is SIGILL, the implementation may
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alternatively define that no action is taken.) Next the equivalent of:</p>
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<pre>
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<tt>(*func)(sig);
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</tt>
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</pre>
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<p>is executed. If and when the function returns, if the value of <i>sig</i> was SIGFPE, SIGILL, or SIGSEGV or any other
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implementation-defined value corresponding to a computational exception, the behavior is undefined. Otherwise, the program shall
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resume execution at the point it was interrupted. If the signal occurs as the result of calling the <a href=
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"../functions/abort.html"><i>abort</i>()</a>, <a href="../functions/raise.html"><i>raise</i>()</a>, <sup>[<a href=
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"javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> <a href=
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"../functions/kill.html"><i>kill</i>()</a>, <a href="../functions/pthread_kill.html"><i>pthread_kill</i>()</a>, or <a href=
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"../functions/sigqueue.html"><i>sigqueue</i>()</a> <img src="../images/opt-end.gif" alt="[Option End]" border="0"> function, the
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signal handler shall not call the <a href="../functions/raise.html"><i>raise</i>()</a> function.</p>
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<p>If the signal occurs other than as the result of calling <a href="../functions/abort.html"><i>abort</i>()</a>, <a href=
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"../functions/raise.html"><i>raise</i>()</a>, <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src=
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"../images/opt-start.gif" alt="[Option Start]" border="0"> <a href="../functions/kill.html"><i>kill</i>()</a>, <a href=
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"../functions/pthread_kill.html"><i>pthread_kill</i>()</a>, or <a href="../functions/sigqueue.html"><i>sigqueue</i>()</a>, <img
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src="../images/opt-end.gif" alt="[Option End]" border="0"> the behavior is undefined if the signal handler refers to any
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object with static storage duration other than by assigning a value to an object declared as volatile <b>sig_atomic_t</b>, or if
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the signal handler calls any function in the standard library other than one of the functions listed in <a href=
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"xsh_chap02_04.html#tag_02_04"><i>Signal Concepts</i></a> . Furthermore, if such a call fails, the value of <i>errno</i> is
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unspecified.</p>
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<p>At program start-up, the equivalent of:</p>
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<pre>
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<tt>signal(</tt><i>sig</i><tt>, SIG_IGN);
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</tt>
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</pre>
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<p>is executed for some signals, and the equivalent of:</p>
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<pre>
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<tt>signal(</tt><i>sig</i><tt>, SIG_DFL);
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</tt>
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</pre>
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<p>is executed for all other signals <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif"
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alt="[Option Start]" border="0"> (see <i><a href="../functions/exec.html">exec</a></i>). <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_690_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If the request can be honored, <i>signal</i>() shall return the value of <i>func</i> for the most recent call to <i>signal</i>()
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for the specified signal <i>sig</i>. Otherwise, SIG_ERR shall be returned and a positive value shall be stored in <i>errno</i>.</p>
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</blockquote>
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<h4><a name="tag_03_690_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>signal</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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The <i>sig</i> argument is not a valid signal number or an attempt is made to catch a signal that cannot be caught or ignore a
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signal that cannot be ignored. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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</dl>
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<p>The <i>signal</i>() function may fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> An
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attempt was made to set the action to SIG_DFL for a signal that cannot be caught or ignored (or both). <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_690_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_690_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <a href="../functions/sigaction.html"><i>sigaction</i>()</a> function provides a more comprehensive and reliable mechanism
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for controlling signals; new applications should use <a href="../functions/sigaction.html"><i>sigaction</i>()</a> rather than
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<i>signal</i>().</p>
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</blockquote>
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<h4><a name="tag_03_690_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_690_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_690_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_04.html#tag_02_04"><i>Signal Concepts</i></a> , <a href="exec.html"><i><a href=
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"../functions/exec.html">exec</a></i>()</a> , <a href="pause.html"><i>pause</i>()</a> , <a href=
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"sigaction.html"><i>sigaction</i>()</a> , <a href="sigsuspend.html"><i>sigsuspend</i>()</a> , <a href=
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"waitid.html"><i>waitid</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/signal.h.html"><i><signal.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_690_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_690_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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<p>The DESCRIPTION is updated to indicate that the <a href="../functions/sigpause.html"><i>sigpause</i>()</a> function restores the
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process' signal mask to its original state before returning.</p>
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<p>The RETURN VALUE section is updated to indicate that the <a href="../functions/sigpause.html"><i>sigpause</i>()</a> function
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suspends execution of the process until a signal is received, whereupon it returns -1 and sets <i>errno</i> to [EINTR].</p>
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</blockquote>
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<h4><a name="tag_03_690_13"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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<p>The DESCRIPTION is updated for alignment with the ISO/IEC 9899:1999 standard.</p>
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<p>References to the <i>wait3</i>() function are removed.</p>
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<p>The <a href="../functions/sighold.html"><i>sighold</i>()</a>, <a href="../functions/sigignore.html"><i>sigignore</i>()</a>, <a
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href="../functions/sigrelse.html"><i>sigrelse</i>()</a>, and <a href="../functions/sigset.html"><i>sigset</i>()</a> functions are
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split out onto their own reference page.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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