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| <head> |
| <title>instance-of</title> |
| <link rel=stylesheet href="opcode.css"> |
| </head> |
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| <body> |
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| <h1>instance-of</h1> |
| |
| <h2>Purpose</h2> |
| |
| <p> |
| Store in the given destination register 1 if the indicated reference is an |
| instance of the given type, or 0 if not. The type must be a reference type (not |
| a primitive type). |
| </p> |
| |
| <h2>Details</h2> |
| |
| <table class="instruc"> |
| <thead> |
| <tr> |
| <th>Op & Format</th> |
| <th>Mnemonic / Syntax</th> |
| <th>Arguments</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td>20 22c</td> |
| <td>instance-of vA, vB, type@CCCC</td> |
| <td><code>A:</code> destination register (4 bits)<br/> |
| <code>B:</code> reference-bearing register (4 bits)<br/> |
| <code>C:</code> type index (16 bits)</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <h2>Constraints</h2> |
| |
| <ul> |
| <li> |
| Both A and B must be a valid register indices for the current stack frame. |
| </li> |
| <li> |
| Register vB must contain a reference value. |
| </li> |
| <li> |
| C must be a valid index into the type constant pool. |
| </li> |
| <li> |
| Type constant pool entry C must contain a valid type descriptor for a |
| reference type. |
| </li> |
| </ul> |
| |
| <h2>Behavior</h2> |
| |
| <ul> |
| <li> |
| An attempt is made to get a reference to the class K the name of which is |
| contained in type pool entry C. |
| </li> |
| <li> |
| If K has not been loaded and resolved before, it is being loaded and |
| resolved. All exceptions that are possible during class loading can occur at |
| this point. |
| </li> |
| <li> |
| The run-time type of the object reference vB is compared against K. The |
| register vA reflects the result: |
| <ul> |
| <li> |
| vA' = 1 if (and only if) vB is not null and vB is assignment compatible |
| with K according to the usual rules of the Java programming language. |
| </li> |
| <li> |
| vA' = 0 otherwise |
| </li> |
| </ul> |
| </li> |
| <li> |
| If v(A-1) is the lower half of a register pair, v(A-1)' becomes undefined. |
| </li> |
| <li> |
| If v(A+1) is the upper half of a register pair, v(A+1)' becomes undefined. |
| </li> |
| |
| <h2>Exceptions</h2> |
| |
| <p> |
| None. |
| </p> |
| |
| </body> |
| </html> |
