perf: string constructor

src/impl/wrapper.cc

@@ -5,8 +5,7 @@
 using ::md5::impl::MD5;
 
 std::string MD5::Digest() const {
-    std::string result {};
+    std::string result(32, 0x00);
-    result.resize(32);
     auto *ptr = reinterpret_cast<const uint8_t *>(&ctx_);
     for (int i = 0; i < 32; ++ptr) {
         result[i++] = HexTable[*ptr >> 4];

test/hash.cc

@@ -262,11 +262,10 @@ const std::array<std::pair<uint8_t, std::string_view>, 256> test_items {{
     {0xff, "11b7aaa64c413d2f0fccf893881c46a2"},
 }};
 
-constexpr std::string build_test_data(uint8_t index) {
+std::string build_test_data(uint8_t index) {
-    std::string data {};
+    std::string data(index, 0x00);
-    data.reserve(index);
     for (uint8_t i = 0; i < index; ++i) {
-        data.push_back(static_cast<char>(i));
+        data[i] = static_cast<char>(i);
     }
     return data;
 };

test/stream.cc

@@ -4,8 +4,7 @@
 using md5::MD5;
 
 TEST(md5sum, stream) {
-    std::string test_data {};
+    std::string test_data(256 * 256, 0x00); // max -> 65536
-    test_data.resize(256 * 256); // max -> 65536
     for (uint64_t i = 0; i < test_data.size(); ++i) {
         test_data[i] = static_cast<char>(i & 0xff);
     }