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<td><a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc14.html">Prev</a> | <a href="Compiling.doc.html">Next</a> | <a href="Lindholm.INDEX.html">Index</a></td><td align=right><i><i>The Java<sup><font size=-2>TM</font></sup> Virtual Machine Specification</i></i></td>
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<a name="wide">
</a><h2>wide</h2>
<a name="wide.Operation"></a>
<b>Operation</h3></b>
<a name="70155"></a>
Extend local variable index by additional bytes<p><Table Border="1">
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<i>wide</i>
<td><a name="87568"></a>
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<i><opcode></i>
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<i>indexbyte1</i>
<td><a name="87568"></a>
<tr><td><a name="70154"></a>
<i>indexbyte2</i>
<td><a name="87568"></a>
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<a name="70156"></a>
where <i><opcode></i> is one of <i>iload</i>, <i>fload</i>, <i>aload</i>, <i>lload</i>, <i>dload</i>, <i>istore</i>, <i>fstore</i>, <i>astore</i>, <i>lstore</i>, <i>dstore</i>, or <i>ret</i><p><Table Border="1">
<tr><td><a name="70161"></a>
<i>wide</i>
<td><a name="87568"></a>
<tr><td><a name="70163"></a>
<i>iinc</i>
<td><a name="87568"></a>
<tr><td><a name="70165"></a>
<i>indexbyte1</i>
<td><a name="87568"></a>
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<i>indexbyte2</i>
<td><a name="87568"></a>
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<i>constbyte1</i>
<td><a name="87568"></a>
<tr><td><a name="70171"></a>
<i>constbyte2</i>
<td><a name="87568"></a>
</Table><br><br><p>
<a name="wide.Forms"></a>
<b>Forms</h3></b>
<a name="70172"></a>
<i>wide</i> = 196 (0xc4)<p>
<a name="wide.Stack"></a>
<b>Stack</h3></b>
<a name="70173"></a>
Same as modified instruction<p>
<a name="wide.Description"></a>
<b>Description</h3></b>
<a name="70174"></a>
The <i>wide</i> instruction modifies the behavior of another instruction. It takes one of two formats, depending on the instruction being modified. The first form of the <i>wide</i> instruction modifies one of the instructions <i>iload</i>, <i>fload</i>, <i>aload</i>, <i>lload</i>, <i>dload</i>, <i>istore</i>, <i>fstore</i>, <i>astore</i>, <i>lstore</i>, <i>dstore</i>, or <i>ret</i>. The second form applies only to the <i>iinc</i> instruction.<p>
In either case, the <i>wide</i> opcode itself is followed in the compiled code by the opcode of the instruction <i>wide</i> modifies. In either form, two unsigned bytes <i>indexbyte1</i> and <i>indexbyte2</i> follow the modified opcode and are assembled into a 16-bit unsigned index to a local variable in the current frame <a href="Overview.doc.html#17257">(§3.6)</a>, where the value of the index is (<i>indexbyte1</i> << 8) | <i>indexbyte2</i>. The calculated index must be a valid index into the local variables of the current frame. Where the <i>wide</i> instruction modifies an <i>lload</i>, <i>dload</i>, <i>lstore</i>, or <i>dstore</i> instruction, the index following the calculated index (index + 1) must also be a valid index into the local variables. In the second form, two immediate unsigned bytes <i>constbyte1</i> and <i>constbyte2</i> follow <i>indexbyte1</i> and <i>indexbyte2</i> in the code stream. Those bytes are also assembled into a signed 16-bit constant, where the constant is (<i>constbyte1</i> << 8) | <i>constbyte2</i>.<p>
<a name="70179"></a>
<a href="Instructions2.doc.html#">The widened bytecode operates as normal, except for the use of the wider index and, in the case of the second form, the larger increment range.</a><p>
<a name="wide.Notes"></a>
<b>Notes</h3></b>
<a name="70183"></a>
Although we say that <i>wide</i> "modifies the behavior of another instruction," the <i>wide</i> instruction effectively treats the modified instruction as operands to <i>wide</i>, denaturing the embedded instruction in the process. In the case of a modified <i>iinc</i> instruction, one of the logical operands of the <i>iinc</i> is not even at the normal offset from the opcode. The embedded instruction must never be executed directly; its opcode must never be the target of any control transfer instruction.<p>
<a name="70184"></a>
<p>
<a name="66864"></a>
<p>
<hr>
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<a href="VMSpecTOC.doc.html">Contents</a> | <a href="Instructions2.doc14.html">Prev</a> | <a href="Compiling.doc.html">Next</a> | <a href="Lindholm.INDEX.html">Index</a>
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<font size = -1>Java Virtual Machine Specification <br>
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