refactor: move util::Xor to Obfuscation().Xor

This is meant to focus the usages to narrow the scope of the obfuscation optimization.

`Obfuscation::Xor` is mostly a move.

Co-authored-by: maflcko <[email protected]>

Author: l0rinc

src/bench/obfuscation.cpp

@@ -4,7 +4,6 @@
 
 #include <bench/bench.h>
 #include <random.h>
-#include <streams.h>
 #include <util/obfuscation.h>
 
 #include <cstddef>
@@ -18,7 +17,7 @@ static void ObfuscationBench(benchmark::Bench& bench)
 
     size_t offset{0};
     bench.batch(data.size()).unit("byte").run([&] {
-        util::Xor(data, key, offset++); // mutated differently each time
+        Obfuscation().Xor(data, key, offset++); // mutated differently each time
         ankerl::nanobench::doNotOptimizeAway(data);
     });
 }

src/streams.cpp

@@ -6,6 +6,7 @@
 #include <span.h>
 #include <streams.h>
 #include <util/fs_helpers.h>
+#include <util/obfuscation.h>
 
 #include <array>
 
@@ -24,7 +25,7 @@ std::size_t AutoFile::detail_fread(std::span<std::byte> dst)
     size_t ret = std::fread(dst.data(), 1, dst.size(), m_file);
     if (!m_obfuscation.empty()) {
         if (!m_position.has_value()) throw std::ios_base::failure("AutoFile::read: position unknown");
-        util::Xor(dst.subspan(0, ret), m_obfuscation, *m_position);
+        Obfuscation().Xor(dst.subspan(0, ret), m_obfuscation, *m_position);
     }
     if (m_position.has_value()) *m_position += ret;
     return ret;
@@ -103,7 +104,7 @@ void AutoFile::write_buffer(std::span<std::byte> src)
     if (!m_file) throw std::ios_base::failure("AutoFile::write_buffer: file handle is nullptr");
     if (m_obfuscation.size()) {
         if (!m_position) throw std::ios_base::failure("AutoFile::write_buffer: obfuscation position unknown");
-        util::Xor(src, m_obfuscation, *m_position); // obfuscate in-place
+        Obfuscation().Xor(src, m_obfuscation, *m_position); // obfuscate in-place
     }
     if (std::fwrite(src.data(), 1, src.size(), m_file) != src.size()) {
         throw std::ios_base::failure("AutoFile::write_buffer: write failed");

src/streams.h

@@ -11,6 +11,7 @@
 #include <span.h>
 #include <support/allocators/zeroafterfree.h>
 #include <util/check.h>
+#include <util/obfuscation.h>
 #include <util/overflow.h>
 #include <util/syserror.h>
 
@@ -27,27 +28,6 @@
 #include <utility>
 #include <vector>
 
-namespace util {
-inline void Xor(std::span<std::byte> write, std::span<const std::byte> key, size_t key_offset = 0)
-{
-    if (key.size() == 0) {
-        return;
-    }
-    key_offset %= key.size();
-
-    for (size_t i = 0, j = key_offset; i != write.size(); i++) {
-        write[i] ^= key[j++];
-
-        // This potentially acts on very many bytes of data, so it's
-        // important that we calculate `j`, i.e. the `key` index in this
-        // way instead of doing a %, which would effectively be a division
-        // for each byte Xor'd -- much slower than need be.
-        if (j == key.size())
-            j = 0;
-    }
-}
-} // namespace util
-
 /* Minimal stream for overwriting and/or appending to an existing byte vector
  *
  * The referenced vector will grow as necessary
@@ -279,7 +259,7 @@ class DataStream
      */
     void Xor(const std::vector<unsigned char>& key)
     {
-        util::Xor(MakeWritableByteSpan(*this), MakeByteSpan(key));
+        Obfuscation().Xor(MakeWritableByteSpan(*this), MakeByteSpan(key));
     }
 
     /** Compute total memory usage of this object (own memory + any dynamic memory). */

src/test/streams_tests.cpp

@@ -24,7 +24,7 @@ BOOST_AUTO_TEST_CASE(xor_roundtrip_random_chunks)
     auto apply_random_xor_chunks{[&](std::span<std::byte> target, std::span<const std::byte, Obfuscation::KEY_SIZE> obfuscation) {
         for (size_t offset{0}; offset < target.size();) {
             const size_t chunk_size{1 + m_rng.randrange(target.size() - offset)};
-            util::Xor(target.subspan(offset, chunk_size), obfuscation, offset);
+            Obfuscation().Xor(target.subspan(offset, chunk_size), obfuscation, offset);
             offset += chunk_size;
         }
     }};
@@ -67,7 +67,7 @@ BOOST_AUTO_TEST_CASE(xor_bytes_reference)
         std::vector actual{expected};
 
         expected_xor(std::span{expected}.subspan(write_offset), key_bytes, key_offset);
-        util::Xor(std::span{actual}.subspan(write_offset), key_bytes, key_offset);
+        Obfuscation().Xor(std::span{actual}.subspan(write_offset), key_bytes, key_offset);
 
         BOOST_CHECK_EQUAL_COLLECTIONS(expected.begin(), expected.end(), actual.begin(), actual.end());
     }

src/util/obfuscation.h

@@ -6,11 +6,29 @@
 #define BITCOIN_UTIL_OBFUSCATION_H
 
 #include <cstdint>
+#include <span.h>
 
 class Obfuscation
 {
 public:
     static constexpr size_t KEY_SIZE{sizeof(uint64_t)};
+
+    void Xor(std::span<std::byte> write, std::span<const std::byte> key, size_t key_offset = 0)
+    {
+        assert(key.size() == KEY_SIZE);
+        key_offset %= KEY_SIZE;
+
+        for (size_t i = 0, j = key_offset; i != write.size(); i++) {
+            write[i] ^= key[j++];
+
+            // This potentially acts on very many bytes of data, so it's
+            // important that we calculate `j`, i.e. the `key` index in this
+            // way instead of doing a %, which would effectively be a division
+            // for each byte Xor'd -- much slower than need be.
+            if (j == KEY_SIZE)
+                j = 0;
+        }
+    }
 };
 
 #endif // BITCOIN_UTIL_OBFUSCATION_H