Bench tests for CKey->EllSwift

Co-Authored-By: Pieter Wuille <bitcoin-dev@wuille.net>

src/Makefile.bench.include

@@ -29,6 +29,7 @@ bench_bench_bitcoin_SOURCES = \
   bench/data.h \
   bench/descriptors.cpp \
   bench/duplicate_inputs.cpp \
+  bench/ellswift.cpp \
   bench/examples.cpp \
   bench/gcs_filter.cpp \
   bench/hashpadding.cpp \

src/bench/ellswift.cpp

@@ -0,0 +1,31 @@
+// Copyright (c) 2022-2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <bench/bench.h>
+
+#include <key.h>
+#include <random.h>
+
+static void EllSwiftCreate(benchmark::Bench& bench)
+{
+    ECC_Start();
+
+    CKey key;
+    key.MakeNewKey(true);
+
+    uint256 entropy = GetRandHash();
+
+    bench.batch(1).unit("pubkey").run([&] {
+        auto ret = key.EllSwiftCreate(AsBytes(Span{entropy}));
+        /* Use the first 32 bytes of the ellswift encoded public key as next private key. */
+        key.Set(UCharCast(ret.data()), UCharCast(ret.data()) + 32, true);
+        assert(key.IsValid());
+        /* Use the last 32 bytes of the ellswift encoded public key as next entropy. */
+        std::copy(ret.begin() + 32, ret.begin() + 64, AsBytePtr(entropy.data()));
+    });
+
+    ECC_Stop();
+}
+
+BENCHMARK(EllSwiftCreate, benchmark::PriorityLevel::HIGH);