Merge bitcoin/bitcoin#19690: util: improve FindByte() performance

72efc26439da9a1344a19569fb0cab01f82ae7d1 util: improve streams.h:FindByte() performance (Larry Ruane)
604df63f6c70b9692b067777ddb38d946ac0b2fc [bench] add streams findbyte (gzhao408)

Pull request description:

  This PR is strictly a performance improvement; there is no functional change. The `CBufferedFile::FindByte()` method searches for the next occurrence of the given byte in the file. Currently, this is done by explicitly inspecting each byte in turn. This PR takes advantage of `std::find()` to do the same more efficiently, improving its CPU runtime by a factor of about 25 in typical use.

ACKs for top commit:
  achow101:
    re-ACK 72efc26439da9a1344a19569fb0cab01f82ae7d1
  stickies-v:
    re-ACK 72efc26439da9a1344a19569fb0cab01f82ae7d1

Tree-SHA512: ddf0bff335cc8aa34f911aa4e0558fa77ce35d963d602e4ab1c63090b4a386faf074548daf06ee829c7f2c760d06eed0125cf4c34e981c6129cea1804eb3b719

1 files changed, 31 insertions, 0 deletions

diff --git a/src/bench/streams_findbyte.cpp b/src/bench/streams_findbyte.cpp
new file mode 100644
index 0000000000..77f5940926
--- /dev/null
+++ b/src/bench/streams_findbyte.cpp
@@ -0,0 +1,31 @@
+// Copyright (c) 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 <util/fs.h>
+#include <streams.h>
+
+static void FindByte(benchmark::Bench& bench)
+{
+    // Setup
+    FILE* file = fsbridge::fopen("streams_tmp", "w+b");
+    const size_t file_size = 200;
+    uint8_t data[file_size] = {0};
+    data[file_size-1] = 1;
+    fwrite(&data, sizeof(uint8_t), file_size, file);
+    rewind(file);
+    CBufferedFile bf(file, /*nBufSize=*/file_size + 1, /*nRewindIn=*/file_size, 0, 0);
+
+    bench.run([&] {
+        bf.SetPos(0);
+        bf.FindByte(std::byte(1));
+    });
+
+    // Cleanup
+    bf.fclose();
+    fs::remove("streams_tmp");
+}
+
+BENCHMARK(FindByte, benchmark::PriorityLevel::HIGH);