bench: Add base_blob compare bench via uint256

Contributed by Sjors in https://github.com/bitcoin/bitcoin/pull/35896#discussion_r3722884353

This benchmark can be run on top of any earlier commit by applying the
diff of this commit before building.

src/bench/CMakeLists.txt

@@ -52,6 +52,7 @@ add_executable(bench_bitcoin
   strencodings.cpp
   txgraph.cpp
   txorphanage.cpp
+  uint256_blob.cpp
   util_time.cpp
   verify_script.cpp
 )

src/bench/uint256_blob.cpp

@@ -0,0 +1,91 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit.
+
+#include <bench/bench.h>
+#include <random.h>
+#include <uint256.h>
+
+#include <compare>
+#include <cstddef>
+#include <utility>
+#include <vector>
+
+namespace {
+
+enum class Difference {
+    NONE,
+    FIRST_BYTE,
+    LAST_BYTE,
+};
+
+constexpr size_t NUM_PAIRS{4'096};
+
+std::vector<std::pair<uint256, uint256>> MakePairs(Difference difference)
+{
+    FastRandomContext rng{/*fDeterministic=*/true};
+    std::vector<std::pair<uint256, uint256>> pairs;
+    pairs.reserve(NUM_PAIRS);
+
+    for (size_t i{0}; i < NUM_PAIRS; ++i) {
+        uint256 lhs{rng.rand256()};
+        uint256 rhs{lhs};
+        if (difference != Difference::NONE) {
+            const size_t position{difference == Difference::FIRST_BYTE ? 0 : uint256::size() - 1};
+            lhs.begin()[position] = i % 2 == 0 ? 0 : 255;
+            rhs.begin()[position] = i % 2 == 0 ? 255 : 0;
+        }
+        pairs.emplace_back(lhs, rhs);
+    }
+    return pairs;
+}
+
+template <typename Comparator>
+void Comparison(benchmark::Bench& bench, Difference difference, Comparator comparator)
+{
+    const auto pairs{MakePairs(difference)};
+    bench.batch(pairs.size()).unit("comparison").run([&] {
+        for (const auto& [lhs, rhs] : pairs) {
+            ankerl::nanobench::doNotOptimizeAway(comparator(lhs, rhs));
+        }
+    });
+}
+
+void Uint256EqualIdentical(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::NONE, [](const uint256& lhs, const uint256& rhs) { return lhs == rhs; });
+}
+
+void Uint256EqualFirstByteDifferent(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::FIRST_BYTE, [](const uint256& lhs, const uint256& rhs) { return lhs == rhs; });
+}
+
+void Uint256EqualLastByteDifferent(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::LAST_BYTE, [](const uint256& lhs, const uint256& rhs) { return lhs == rhs; });
+}
+
+void Uint256LessIdentical(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::NONE, [](const uint256& lhs, const uint256& rhs) { return lhs < rhs; });
+}
+
+void Uint256LessFirstByteDifferent(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::FIRST_BYTE, [](const uint256& lhs, const uint256& rhs) { return lhs < rhs; });
+}
+
+void Uint256LessLastByteDifferent(benchmark::Bench& bench)
+{
+    Comparison(bench, Difference::LAST_BYTE, [](const uint256& lhs, const uint256& rhs) { return lhs < rhs; });
+}
+
+} // namespace
+
+BENCHMARK(Uint256EqualIdentical);
+BENCHMARK(Uint256EqualFirstByteDifferent);
+BENCHMARK(Uint256EqualLastByteDifferent);
+BENCHMARK(Uint256LessIdentical);
+BENCHMARK(Uint256LessFirstByteDifferent);
+BENCHMARK(Uint256LessLastByteDifferent);