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| <head> |
| <title>array-length</title> |
| <link rel=stylesheet href="opcode.css"> |
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| <body> |
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| <h1>array-length</h1> |
| |
| <h2>Purpose</h2> |
| |
| <p> |
| Store in the given destination register the length of the indicated array, |
| in entries. |
| </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>21 12x</td> |
| <td>array-length vA, vB</td> |
| <td><code>A:</code> destination register (4 bits)<br/> |
| <code>B:</code> array reference-bearing register (4 bits)</td> |
| </tr> |
| </tbody> |
| </table> |
| |
| <h2>Constraints</h2> |
| |
| <ul> |
| <li> |
| Both A and B must be valid register indices for the current stack frame. |
| </li> |
| <li> |
| Register vB must contain a reference to an array. |
| </li> |
| </ul> |
| |
| <h2>Behavior</h2> |
| |
| <ul> |
| <li> |
| The length of the array referenced by vB is stored in vA, that is |
| vA' = length(vB). |
| </li> |
| <li> |
| If register v(A-1) is the lower half of a register pair, register v(A-1)' |
| becomes undefined. |
| </li> |
| <li> |
| If register v(A+1) is the upper half of a register pair, register v(A+1)' |
| becomes undefined. |
| </li> |
| </ul> |
| |
| <h2>Exceptions</h2> |
| |
| <ul> |
| <li> |
| NullPointerException is thrown if the value of register vB is null. |
| </li> |
| </ul> |
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