StringUtil: Speed up EncodeHex()/append_hex()

src/common/small_string.cpp

@@ -181,16 +181,40 @@ void SmallStringBase::append(const char* str, u32 length)
   m_buffer[m_length] = 0;
 }
 
-void SmallStringBase::append_hex(const void* data, size_t len)
+void SmallStringBase::append_hex(const void* data, size_t len, bool comma_separate)
 {
   if (len == 0)
     return;
 
-  make_room_for(static_cast<u32>(len) * 4);
+  static constexpr auto hex_char = [](char x) { return (x >= 0xA) ? ((x - 0xA) + 'a') : (x + '0'); };
   const u8* bytes = static_cast<const u8*>(data);
-  append_format("{:02X}", bytes[0]);
+
+  if (!comma_separate)
+  {
+    make_room_for(static_cast<u32>(len) * 2);
+    for (size_t i = 0; i < len; i++)
+    {
+      m_buffer[m_length++] = hex_char(bytes[i] >> 4);
+      m_buffer[m_length++] = hex_char(bytes[i] & 0xF);
+    }
+  }
+  else
+  {
+    make_room_for(4 + static_cast<u32>(len - 1) * 6);
+    m_buffer[m_length++] = '0';
+    m_buffer[m_length++] = 'x';
+    m_buffer[m_length++] = hex_char(bytes[0] >> 4);
+    m_buffer[m_length++] = hex_char(bytes[0] & 0xF);
     for (size_t i = 1; i < len; i++)
-    append_format(", {:02X}", bytes[i]);
+    {
+      m_buffer[m_length++] = ',';
+      m_buffer[m_length++] = ' ';
+      m_buffer[m_length++] = '0';
+      m_buffer[m_length++] = 'x';
+      m_buffer[m_length++] = hex_char(bytes[i] >> 4);
+      m_buffer[m_length++] = hex_char(bytes[i] & 0xF);
+    }
+  }
 }
 
 void SmallStringBase::prepend(const char* str, u32 length)

src/common/small_string.h

@@ -67,7 +67,7 @@ public:
   void append_format(fmt::format_string<T...> fmt, T&&... args);
 
   // append hex string
-  void append_hex(const void* data, size_t len);
+  void append_hex(const void* data, size_t len, bool comma_separate = false);
 
   // append a single character to this string
   void prepend(char c);

src/common/string_util.cpp

@@ -169,13 +169,20 @@ std::optional<std::vector<u8>> StringUtil::DecodeHex(const std::string_view in)
   return {data};
 }
 
-std::string StringUtil::EncodeHex(const u8* data, int length)
+std::string StringUtil::EncodeHex(const void* data, size_t length)
 {
-  std::stringstream ss;
+  static constexpr auto hex_char = [](char x) { return (x >= 0xA) ? ((x - 0xA) + 'a') : (x + '0'); };
-  for (int i = 0; i < length; i++)
-    ss << std::hex << std::setfill('0') << std::setw(2) << static_cast<int>(data[i]);
 
-  return ss.str();
+  const u8* bytes = static_cast<const u8*>(data);
+
+  std::string ret;
+  ret.reserve(length * 2);
+  for (size_t i = 0; i < length; i++)
+  {
+    ret.push_back(hex_char(bytes[i] >> 4));
+    ret.push_back(hex_char(bytes[i] & 0xF));
+  }
+  return ret;
 }
 
 std::string_view StringUtil::StripWhitespace(const std::string_view str)

src/common/string_util.h

@@ -204,7 +204,12 @@ inline std::string ToChars(bool value, int base)
 
 /// Encode/decode hexadecimal byte buffers
 std::optional<std::vector<u8>> DecodeHex(const std::string_view str);
-std::string EncodeHex(const u8* data, int length);
+std::string EncodeHex(const void* data, size_t length);
+template<typename T>
+ALWAYS_INLINE static std::string EncodeHex(const std::span<const T> data)
+{
+  return EncodeHex(data.data(), data.size_bytes());
+}
 
 /// Returns true if the character is a hexadecimal digit.
 template<typename T>