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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.doc47.html">Prev</a> | <a href="Instructions2.doc49.html">Next</a> | <a href="Mnemonics.doc.html">Index</a><hr><br> <a name="dup2_x2"></a><h2>dup2_x2</h2><a name="dup2_x2.Operation"></a><b>Operation</b><br><a name="67864"></a>Duplicate top two operand stack words and put four down<p><Table Border="3"><tr><td><a name="67863"></a> <i>dup2_x2</i><td><a name="87568"></a> </Table><Table><tr><td></Table><p><a name="dup2_x2.Forms"></a><b>Forms</b><br><a name="67865"></a><i>dup2_x2</i> = 94 (0x5e)<p><a name="dup2_x2.Stack"></a><b>Stack</b><br><a name="67866"></a>...,<em> </em><i>word4</i>, <i>word3</i>, <i>word2</i>, <i>word1</i> <img src="chars/arrwdbrt.gif"> ...<em>, </em><i>word2</i>, <i>word1</i>, <i>word4</i>, <i>word3</i>, <i>word2</i>, <i>word1</i><p><a name="dup2_x2.Description"></a><b>Description</b><br><a name="67867"></a>The top two words on the operand stack are duplicated and the copies inserted, in the original order, four words down in the operand stack.<p><a name="67868"></a>The <i>dup2_x2</i> instruction must not be used unless each of <i>word1</i> and <i>word2</i> is a 32-bit data type or both together are the two words of a single 64-bit datum, and unless <i>word3</i> and <i>word4</i> are each a word that contains a 32-bit data type or both together are the two words of a single 64-bit datum.<p><a name="dup2_x2.Notes"></a><b>Notes</b><br><a name="67869"></a>Except for restrictions preserving the integrity of 64-bit data types, the <i>dup2_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.doc47.html">Prev</a> | <a href="Instructions2.doc49.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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