[libcxx-commits] [libcxx] [libc++] Introduce one-sided binary search for set_intersection so that it can be completed in sub-linear time for a large class of inputs. (PR #75230)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,223 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <algorithm>
+#include <iterator>
+#include <set>
+#include <stdlib.h>
+#include <vector>
+
+#include "common.h"
+#include "test_iterators.h"
+
+namespace {
+
+// types of containers we'll want to test, covering interesting iterator types
+struct VectorContainer {
+  template <typename... Args>
+  using type = std::vector<Args...>;
+
+  static constexpr const char* Name = "Vector";
+};
+
+struct SetContainer {
+  template <typename... Args>
+  using type = std::set<Args...>;
+
+  static constexpr const char* Name = "Set";
+};
+
+using AllContainerTypes = std::tuple<VectorContainer, SetContainer>;
+
+// set_intersection performance may depend on where matching values lie
+enum class OverlapPosition {
+  None,
+  Front,
+  // performance-wise, matches at the back are identical to ones at the front
+  Interlaced,
+};
+
+struct AllOverlapPositions : EnumValuesAsTuple<AllOverlapPositions, OverlapPosition, 3> {
+  static constexpr const char* Names[] = {"None", "Front", "Interlaced"};
+};
+
+// functor that moves elements from an iterator range into a new Container instance
+template <typename Container>
+struct MoveInto {
+  template <class It>
+  [[nodiscard]] static Container operator()(It first, It last) {
+    Container out;
+    std::move(first, last, std::inserter(out, out.begin()));
+    return out;
+  }
+};
+
+// lightweight wrapping around fillValues() which puts a little effort into
+// making that would be contiguous when sorted non-contiguous in memory
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ldionne wrote:

I think this sentence is missing a few words.

https://github.com/llvm/llvm-project/pull/75230