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</pre><pre class="rust"><code><span class="kw">use</span> <span class="ident">std::ops</span>::{<span class="ident">AddAssign</span>, <span class="ident">MulAssign</span>};
<span class="comment">// For implementing base10_digits() accessor on LitInt.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BigInt</span> {
<span class="ident">digits</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span>,
}
<span class="kw">impl</span> <span class="ident">BigInt</span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() -&gt; <span class="self">Self</span> {
<span class="ident">BigInt</span> { <span class="ident">digits</span>: <span class="ident">Vec::new</span>() }
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">to_string</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="ident">String</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">repr</span> <span class="op">=</span> <span class="ident">String::with_capacity</span>(<span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">len</span>());
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">has_nonzero</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="kw">for</span> <span class="ident">digit</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">iter</span>().<span class="ident">rev</span>() {
<span class="ident">has_nonzero</span> <span class="op">|</span><span class="op">=</span> <span class="kw-2">*</span><span class="ident">digit</span> <span class="op">!</span><span class="op">=</span> <span class="number">0</span>;
<span class="kw">if</span> <span class="ident">has_nonzero</span> {
<span class="ident">repr</span>.<span class="ident">push</span>((<span class="kw-2">*</span><span class="ident">digit</span> <span class="op">+</span> <span class="string">b&#39;0&#39;</span>) <span class="kw">as</span> <span class="ident">char</span>);
}
}
<span class="kw">if</span> <span class="ident">repr</span>.<span class="ident">is_empty</span>() {
<span class="ident">repr</span>.<span class="ident">push</span>(<span class="string">&#39;0&#39;</span>);
}
<span class="ident">repr</span>
}
<span class="kw">fn</span> <span class="ident">reserve_two_digits</span>(<span class="kw-2">&amp;mut</span> <span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">len</span>();
<span class="kw">let</span> <span class="ident">desired</span> <span class="op">=</span>
<span class="ident">len</span> <span class="op">+</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">ends_with</span>(<span class="kw-2">&amp;</span>[<span class="number">0</span>, <span class="number">0</span>]) <span class="kw">as</span> <span class="ident">usize</span> <span class="op">+</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">ends_with</span>(<span class="kw-2">&amp;</span>[<span class="number">0</span>]) <span class="kw">as</span> <span class="ident">usize</span>;
<span class="self">self</span>.<span class="ident">digits</span>.<span class="ident">resize</span>(<span class="ident">desired</span>, <span class="number">0</span>);
}
}
<span class="kw">impl</span> <span class="ident">AddAssign</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BigInt</span> {
<span class="comment">// Assumes increment &lt;16.</span>
<span class="kw">fn</span> <span class="ident">add_assign</span>(<span class="kw-2">&amp;mut</span> <span class="self">self</span>, <span class="kw-2">mut</span> <span class="ident">increment</span>: <span class="ident">u8</span>) {
<span class="self">self</span>.<span class="ident">reserve_two_digits</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">i</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">while</span> <span class="ident">increment</span> <span class="op">&gt;</span> <span class="number">0</span> {
<span class="kw">let</span> <span class="ident">sum</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">digits</span>[<span class="ident">i</span>] <span class="op">+</span> <span class="ident">increment</span>;
<span class="self">self</span>.<span class="ident">digits</span>[<span class="ident">i</span>] <span class="op">=</span> <span class="ident">sum</span> <span class="op">%</span> <span class="number">10</span>;
<span class="ident">increment</span> <span class="op">=</span> <span class="ident">sum</span> <span class="op">/</span> <span class="number">10</span>;
<span class="ident">i</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
}
}
}
<span class="kw">impl</span> <span class="ident">MulAssign</span><span class="op">&lt;</span><span class="ident">u8</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">BigInt</span> {
<span class="comment">// Assumes base &lt;=16.</span>
<span class="kw">fn</span> <span class="ident">mul_assign</span>(<span class="kw-2">&amp;mut</span> <span class="self">self</span>, <span class="ident">base</span>: <span class="ident">u8</span>) {
<span class="self">self</span>.<span class="ident">reserve_two_digits</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">carry</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">for</span> <span class="ident">digit</span> <span class="kw">in</span> <span class="kw-2">&amp;mut</span> <span class="self">self</span>.<span class="ident">digits</span> {
<span class="kw">let</span> <span class="ident">prod</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">digit</span> <span class="op">*</span> <span class="ident">base</span> <span class="op">+</span> <span class="ident">carry</span>;
<span class="kw-2">*</span><span class="ident">digit</span> <span class="op">=</span> <span class="ident">prod</span> <span class="op">%</span> <span class="number">10</span>;
<span class="ident">carry</span> <span class="op">=</span> <span class="ident">prod</span> <span class="op">/</span> <span class="number">10</span>;
}
}
}
</code></pre></div>
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