From b7489ecb52c1f99facb7c81c5e46963394d0620d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <lorinc.pap@gmail.com>
Date: Tue, 20 Feb 2024 15:59:41 +0100
Subject: [PATCH 1/2] Add benchmark for TryParseHex

Running `make && ./src/bench/bench_bitcoin -filter=HexParse` a few times results in:
```
|           ns/base16 |            base16/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                1.60 |      623,238,893.11 |    0.3% |      0.01 | `HexParse`
|                1.65 |      606,747,566.34 |    0.6% |      0.01 | `HexParse`
|                1.60 |      626,149,544.07 |    0.3% |      0.01 | `HexParse`
```
---
 src/Makefile.bench.include |  1 +
 src/bench/parse_hex.cpp    | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 src/bench/parse_hex.cpp

diff --git a/src/Makefile.bench.include b/src/Makefile.bench.include
index b24405ce19c..4d814bc5dc9 100644
--- a/src/Makefile.bench.include
+++ b/src/Makefile.bench.include
@@ -42,6 +42,7 @@ bench_bench_bitcoin_SOURCES = \
   bench/merkle_root.cpp \
   bench/nanobench.cpp \
   bench/nanobench.h \
+  bench/parse_hex.cpp \
   bench/peer_eviction.cpp \
   bench/poly1305.cpp \
   bench/pool.cpp \
diff --git a/src/bench/parse_hex.cpp b/src/bench/parse_hex.cpp
new file mode 100644
index 00000000000..db3ead043c8
--- /dev/null
+++ b/src/bench/parse_hex.cpp
@@ -0,0 +1,36 @@
+// Copyright (c) 2024- 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 <random.h>
+#include <stddef.h>
+#include <util/strencodings.h>
+#include <cassert>
+#include <optional>
+#include <vector>
+
+std::string generateHexString(size_t length) {
+    const auto hex_digits = "0123456789ABCDEF";
+    FastRandomContext rng(/*fDeterministic=*/true);
+
+    std::string data;
+    while (data.size() < length) {
+        auto digit = hex_digits[rng.randbits(4)];
+        data.push_back(digit);
+    }
+    return data;
+}
+
+static void HexParse(benchmark::Bench& bench)
+{
+    auto data = generateHexString(130); // Generates 678B0EDA0A1FD30904D5A65E3568DB82DB2D918B0AD8DEA18A63FECCB877D07CAD1495C7157584D877420EF38B8DA473A6348B4F51811AC13C786B962BEE5668F9 by default
+
+    bench.batch(data.size()).unit("base16").run([&] {
+        auto result = TryParseHex(data);
+        assert(result != std::nullopt); // make sure we're measuring the successful case
+        ankerl::nanobench::doNotOptimizeAway(result);
+    });
+}
+
+BENCHMARK(HexParse, benchmark::PriorityLevel::HIGH);

From a19235c14b3dc02de30b5d769de29d1752c23dbd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <lorinc.pap@gmail.com>
Date: Sun, 25 Feb 2024 17:50:25 +0100
Subject: [PATCH 2/2] Preallocate result in `TryParseHex` to avoid resizing

Running `make && ./src/bench/bench_bitcoin -filter=HexParse` a few times results in:
```
|           ns/base16 |            base16/s |    err% |     total | benchmark
|--------------------:|--------------------:|--------:|----------:|:----------
|                0.68 |    1,465,555,976.27 |    0.8% |      0.01 | `HexParse`
|                0.68 |    1,472,962,920.18 |    0.3% |      0.01 | `HexParse`
|                0.68 |    1,476,159,423.00 |    0.3% |      0.01 | `HexParse`
```
---
 src/util/strencodings.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/util/strencodings.cpp b/src/util/strencodings.cpp
index a54f408496b..b51b283a69e 100644
--- a/src/util/strencodings.cpp
+++ b/src/util/strencodings.cpp
@@ -81,6 +81,8 @@ template <typename Byte>
 std::optional<std::vector<Byte>> TryParseHex(std::string_view str)
 {
     std::vector<Byte> vch;
+    vch.reserve(str.size() / 2); // two hex characters form a single byte
+
     auto it = str.begin();
     while (it != str.end()) {
         if (IsSpace(*it)) {