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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.doc46.html">Prev</a> | <a href="Instructions2.doc48.html">Next</a> | <a href="Mnemonics.doc.html">Index</a><hr><br> <a name="dup2_x1"></a><h2>dup2_x1</h2><a name="dup2_x1.Operation"></a><b>Operation</b><br><a name="67852"></a>Duplicate top two operand stack words and put three down<p><Table Border="3"><tr><td><a name="67851"></a> <i>dup2_x1</i><td><a name="87568"></a> </Table><Table><tr><td></Table><p><a name="dup2_x1.Forms"></a><b>Forms</b><br><a name="67853"></a><i>dup2_x1</i> = 93 (0x5d)<p><a name="dup2_x1.Stack"></a><b>Stack</b><br><a name="67854"></a>..., <i>word3</i>, <i>word2</i>, <i>word1</i> <img src="chars/arrwdbrt.gif"> ..., <i>word2</i><em>, </em><i>word1</i>, <i>word3</i>, <i>word2</i>, <i>word1</i><p><a name="dup2_x1.Description"></a><b>Description</b><br><a name="67855"></a>The top two words on the operand stack are duplicated and the copies inserted, in the original order, three words down in the operand stack. <p><a name="67856"></a>The <i>dup2_x1</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 that contain a single 64-bit datum, and unless <i>word3</i> is a word that contains a 32-bit data type.<p><a name="dup2_x1.Notes"></a><b>Notes</b><br><a name="67857"></a>Except for restrictions preserving the integrity of 64-bit data types, the <i>dup2_x1</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.doc46.html">Prev</a> | <a href="Instructions2.doc48.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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