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<span class="comment">// Copyright 2012-2017 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="kw">use</span> <span class="ident">cmp</span>;
<span class="kw">use</span> <span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">ptr</span>;
<span class="doccomment">/// Rotation is much faster if it has access to a little bit of memory. This</span>
<span class="doccomment">/// union provides a RawVec-like interface, but to a fixed-size stack buffer.</span>
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">unions_with_drop_fields</span>)]</span>
<span class="ident">union</span> <span class="ident">RawArray</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Ensure this is appropriately aligned for T, and is big</span>
<span class="doccomment">/// enough for two elements even if T is enormous.</span>
<span class="ident">typed</span>: [<span class="ident">T</span>; <span class="number">2</span>],
<span class="doccomment">/// For normally-sized types, especially things like u8, having more</span>
<span class="doccomment">/// than 2 in the buffer is necessary for usefulness, so pad it out</span>
<span class="doccomment">/// enough to be helpful, but not so big as to risk overflow.</span>
<span class="ident">_extra</span>: [<span class="ident">usize</span>; <span class="number">32</span>],
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">RawArray</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="self">Self</span> {
<span class="kw">unsafe</span> { <span class="ident">mem</span>::<span class="ident">uninitialized</span>() }
}
<span class="kw">fn</span> <span class="ident">ptr</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">typed</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> }
}
<span class="kw">fn</span> <span class="ident">cap</span>() <span class="op">-></span> <span class="ident">usize</span> {
<span class="kw">if</span> <span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">==</span> <span class="number">0</span> {
<span class="ident">usize</span>::<span class="ident">max_value</span>()
} <span class="kw">else</span> {
<span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="self">Self</span><span class="op">></span>() <span class="op">/</span> <span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>()
}
}
}
<span class="doccomment">/// Rotates the range `[mid-left, mid+right)` such that the element at `mid`</span>
<span class="doccomment">/// becomes the first element. Equivalently, rotates the range `left`</span>
<span class="doccomment">/// elements to the left or `right` elements to the right.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The specified range must be valid for reading and writing.</span>
<span class="doccomment">/// The type `T` must have non-zero size.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Algorithm</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For longer rotations, swap the left-most `delta = min(left, right)`</span>
<span class="doccomment">/// elements with the right-most `delta` elements. LLVM vectorizes this,</span>
<span class="doccomment">/// which is profitable as we only reach this step for a "large enough"</span>
<span class="doccomment">/// rotation. Doing this puts `delta` elements on the larger side into the</span>
<span class="doccomment">/// correct position, leaving a smaller rotate problem. Demonstration:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```text</span>
<span class="doccomment">/// [ 6 7 8 9 10 11 12 13 . 1 2 3 4 5 ]</span>
<span class="doccomment">/// 1 2 3 4 5 [ 11 12 13 . 6 7 8 9 10 ]</span>
<span class="doccomment">/// 1 2 3 4 5 [ 8 9 10 . 6 7 ] 11 12 13</span>
<span class="doccomment">/// 1 2 3 4 5 6 7 [ 10 . 8 9 ] 11 12 13</span>
<span class="doccomment">/// 1 2 3 4 5 6 7 [ 9 . 8 ] 10 11 12 13</span>
<span class="doccomment">/// 1 2 3 4 5 6 7 8 [ . ] 9 10 11 12 13</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Once the rotation is small enough, copy some elements into a stack</span>
<span class="doccomment">/// buffer, `memmove` the others, and move the ones back from the buffer.</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">ptr_rotate</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">mut</span> <span class="ident">left</span>: <span class="ident">usize</span>, <span class="ident">mid</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>, <span class="kw-2">mut</span> <span class="ident">right</span>: <span class="ident">usize</span>) {
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="ident">delta</span> <span class="op">=</span> <span class="ident">cmp</span>::<span class="ident">min</span>(<span class="ident">left</span>, <span class="ident">right</span>);
<span class="kw">if</span> <span class="ident">delta</span> <span class="op"><=</span> <span class="ident">RawArray</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>::<span class="ident">cap</span>() {
<span class="kw">break</span>;
}
<span class="ident">ptr</span>::<span class="ident">swap_nonoverlapping</span>(
<span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)),
<span class="ident">mid</span>.<span class="ident">offset</span>((<span class="ident">right</span><span class="op">-</span><span class="ident">delta</span>) <span class="kw">as</span> <span class="ident">isize</span>),
<span class="ident">delta</span>);
<span class="kw">if</span> <span class="ident">left</span> <span class="op"><=</span> <span class="ident">right</span> {
<span class="ident">right</span> <span class="op">-=</span> <span class="ident">delta</span>;
} <span class="kw">else</span> {
<span class="ident">left</span> <span class="op">-=</span> <span class="ident">delta</span>;
}
}
<span class="kw">let</span> <span class="ident">rawarray</span> <span class="op">=</span> <span class="ident">RawArray</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="ident">buf</span> <span class="op">=</span> <span class="ident">rawarray</span>.<span class="ident">ptr</span>();
<span class="kw">let</span> <span class="ident">dim</span> <span class="op">=</span> <span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)).<span class="ident">offset</span>(<span class="ident">right</span> <span class="kw">as</span> <span class="ident">isize</span>);
<span class="kw">if</span> <span class="ident">left</span> <span class="op"><=</span> <span class="ident">right</span> {
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(<span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)), <span class="ident">buf</span>, <span class="ident">left</span>);
<span class="ident">ptr</span>::<span class="ident">copy</span>(<span class="ident">mid</span>, <span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)), <span class="ident">right</span>);
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(<span class="ident">buf</span>, <span class="ident">dim</span>, <span class="ident">left</span>);
}
<span class="kw">else</span> {
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(<span class="ident">mid</span>, <span class="ident">buf</span>, <span class="ident">right</span>);
<span class="ident">ptr</span>::<span class="ident">copy</span>(<span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)), <span class="ident">dim</span>, <span class="ident">left</span>);
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(<span class="ident">buf</span>, <span class="ident">mid</span>.<span class="ident">offset</span>(<span class="op">-</span>(<span class="ident">left</span> <span class="kw">as</span> <span class="ident">isize</span>)), <span class="ident">right</span>);
}
}
</pre>
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