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📁 Jvm 规范说明。The Java Virtual Machine was designed to support the Java programming language. Some concep

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<html><head><title>VM Spec  </title></head><body BGCOLOR=#eeeeff text=#000000 LINK=#0000ff VLINK=#000077 ALINK=#ff0000> <a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc44.html">Prev</a> | <a href="Instructions2.doc46.html">Next</a> | <a href="Mnemonics.doc.html">Index</a><hr><br> <a name="dup_x2"></a><h2>dup_x2</h2><a name="dup_x2.Operation"></a><b>Operation</b><br><a name="67819"></a>Duplicate top operand stack word and put three down<p><Table Border="3"><tr><td><a name="67818"></a> <i>dup_x2</i><td><a name="87568"></a> </Table><Table><tr><td></Table><p><a name="dup_x2.Forms"></a><b>Forms</b><br><a name="67820"></a><i>dup_x2</i><em> </em>= 91 (0x5b)<p><a name="dup_x2.Stack"></a><b>Stack</b><br><a name="67821"></a>..., <i>word3</i>, <i>word2</i>, <i>word1</i> <img src="chars/arrwdbrt.gif"> ...<em>, </em><i>word1</i>, <i>word3</i>, <i>word2</i>, <i>word1</i><p><a name="dup_x2.Description"></a><b>Description</b><br><a name="67822"></a>The top word on the operand stack is duplicated and the copy inserted three words down in the operand stack. <p><a name="67823"></a>The <i>dup_x2</i> instruction must not be used unless each of <i>word2</i> and <i>word3</i> is a word that contains a 32-bit data type or together are the two words of a single 64-bit datum, and unless <i>word1</i> contains a 32-bit data type.<p><a name="dup_x2.Notes"></a><b>Notes</b><br><a name="67824"></a>Except for restrictions preserving the integrity of 64-bit data types, the <i>dup_x2</i> instruction operates on untyped words, ignoring the types of the data they contain.<p><hr><!-- This inserts footnotes--><p><a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc44.html">Prev</a> | <a href="Instructions2.doc46.html">Next</a> | <a href="Mnemonics.doc.html">Index</a><p><font size=-1>Java Virtual Machine Specification (HTML generated by dkramer on February 25, 1997)<br><i><a href="Copyright.doc.html">Copyright &#169 1996 Sun Microsystems, Inc.</a>All rights reserved</i><br>Please send any comments or corrections to <a href="mailto:doug.kramer@sun.com">doug.kramer@sun.com</a></font></body></html>

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