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      6 <title>instance-of</title>
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     10 <body>
     11 
     12 <h1>instance-of</h1>
     13 
     14 <h2>Purpose</h2>
     15 
     16 <p>
     17 Store in the given destination register 1 if the indicated reference is an
     18 instance of the given type, or 0 if not. The type must be a reference type (not
     19 a primitive type).
     20 </p>
     21 
     22 <h2>Details</h2>
     23 
     24 <table class="instruc">
     25 <thead>
     26 <tr>
     27   <th>Op &amp; Format</th>
     28   <th>Mnemonic / Syntax</th>
     29   <th>Arguments</th>
     30 </tr>
     31 </thead>
     32 <tbody>
     33 <tr>
     34   <td>20 22c</td>
     35   <td>instance-of vA, vB, type@CCCC</td>
     36   <td><code>A:</code> destination register (4 bits)<br/>
     37     <code>B:</code> reference-bearing register (4 bits)<br/>
     38     <code>C:</code> type index (16 bits)</td>
     39 </tr>
     40 </tbody>
     41 </table>
     42 
     43 <h2>Constraints</h2>
     44 
     45 <ul>
     46   <li>
     47     Both A and B must be a valid register indices for the current stack frame.
     48   </li>
     49   <li>
     50     Register vB must contain a reference value.
     51   </li>
     52   <li>
     53     C must be a valid index into the type constant pool.
     54   </li>
     55   <li>
     56     Type constant pool entry C must contain a valid type descriptor for a
     57     reference type.
     58   </li> 
     59 </ul>
     60 
     61 <h2>Behavior</h2>
     62 
     63 <ul>
     64   <li>
     65     An attempt is made to get a reference to the class K the name of which is
     66     contained in type pool entry C.
     67   </li>
     68   <li>
     69     If K has not been loaded and resolved before, it is being loaded and
     70     resolved. All exceptions that are possible during class loading can occur at
     71     this point.
     72   </li>
     73   <li>
     74     The run-time type of the object reference vB is compared against K. The
     75     register vA reflects the result:
     76     <ul>
     77       <li>
     78         vA' = 1 if (and only if) vB is not null and vB is assignment compatible
     79         with K according to the usual rules of the Java programming language.
     80       </li>
     81       <li>
     82         vA' = 0 otherwise
     83       </li>
     84     </ul>
     85   </li>
     86   <li>
     87     If v(A-1) is the lower half of a register pair, v(A-1)' becomes undefined.
     88   </li>
     89   <li>
     90     If v(A+1) is the upper half of a register pair, v(A+1)' becomes undefined.
     91   </li> 
     92 
     93 <h2>Exceptions</h2>
     94 
     95 <p>
     96 None.
     97 </p>
     98 
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