[libc++] Replace modulus operations in std::seed_seq::generate with conditional checks.
Abseil benchmarks suggest that the conditional checks result in faster code (4-5x)
as they are compiled into conditional move instructions (cmov on x86).
Reviewed By: #libc, philnik, Mordante
Spies: pengfei, Mordante, philnik, libcxx-commits
Differential Revision: https://reviews.llvm.org/D125329
NOKEYCHECK=True
GitOrigin-RevId: b07880454ba32e48a2e7f7be35516e0b76f60077
diff --git a/benchmarks/random.bench.cpp b/benchmarks/random.bench.cpp
new file mode 100644
index 0000000..e437849
--- /dev/null
+++ b/benchmarks/random.bench.cpp
@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+// 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 <array>
+#include <cstddef>
+#include <functional>
+#include <random>
+
+#include "benchmark/benchmark.h"
+
+constexpr std::size_t MAX_BUFFER_LEN = 256;
+constexpr std::size_t MAX_SEED_LEN = 16;
+
+static void BM_SeedSeq_Generate(benchmark::State& state) {
+ std::array<std::uint32_t, MAX_BUFFER_LEN> buffer;
+ std::array<std::uint32_t, MAX_SEED_LEN> seeds;
+ {
+ std::random_device rd;
+ std::generate(std::begin(seeds), std::begin(seeds) + state.range(0), [&]() { return rd(); });
+ }
+ std::seed_seq seed(std::begin(seeds), std::begin(seeds) + state.range(0));
+ for (auto _ : state) {
+ seed.generate(std::begin(buffer), std::begin(buffer) + state.range(1));
+ }
+}
+BENCHMARK(BM_SeedSeq_Generate)->Ranges({{1, MAX_SEED_LEN}, {1, MAX_BUFFER_LEN}});
+
+BENCHMARK_MAIN();