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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.doc45.html">Prev</a> | <a href="Instructions2.doc47.html">Next</a> | <a href="Mnemonics.doc.html">Index</a><hr><br> <a name="dup2"></a><h2>dup2</h2><a name="dup2.Operation"></a><b>Operation</b><br><a name="67834"></a>Duplicate top two operand stack word<p><Table Border="3"><tr><td><a name="67833"></a> <i>dup2</i><td><a name="87568"></a> </Table><Table><tr><td></Table>s<p><a name="dup2.Forms"></a><b>Forms</b><br><a name="67835"></a><i>dup2</i> = 92 (0x5c)<p><a name="dup2.Stack"></a><b>Stack</b><br><a name="67836"></a>..., <i>word2</i>, <i>word1</i> <img src="chars/arrwdbrt.gif"> ..., <i>word2</i>, <i>word1</i><em>, </em><i>word2</i>, <i>word1</i><p><a name="dup2.Description"></a><b>Description</b><br><a name="67837"></a>The top two words on the operand stack are duplicated and pushed onto the operand stack, in the original order. <p><a name="67838"></a>The <i>dup2</i> instruction must not be used unless each of <i>word1</i> and <i>word2</i> is 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.Notes"></a><b>Notes</b><br><a name="67839"></a>Except for restrictions preserving the integrity of 64-bit data types, the <i>dup2</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.doc45.html">Prev</a> | <a href="Instructions2.doc47.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 © 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>?? 快捷鍵說明
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