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<title>array-length</title>
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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>
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<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>
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<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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