uncates the length of <code class="code">b</code> to <code class="code">len</code>
  Note: the internal byte sequence is not shortened.
  Raise <code class="code"><span class="constructor">Invalid_argument</span></code> if <code class="code">len&nbsp;&lt;&nbsp;0</code> or <code class="code">len&nbsp;&gt;&nbsp;length&nbsp;b</code>.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.05.0</li>
</ul>
</div>
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