refactor cpp_escape

Author: huangminghuang

protoc-plugin/hpp_gen.cpp

@@ -152,53 +152,36 @@ std::string cpp_escape(std::string_view src) {
   }
   std::string result;
   result.reserve(escaped_len);
-  auto itr = std::back_inserter(result);
+  static const char *const escapedChars[256] = {
+      "\\\\000", "\\\\001", "\\\\002", "\\\\003", "\\\\004", "\\\\005", "\\\\006", "\\\a",    "\\\b",    "\\\t",
+      "\\\n",    "\\\v",    "\\\f",    "\\\r",    "\\\\016", "\\\\017", "\\\\020", "\\\\021", "\\\\022", "\\\\023",
+      "\\\\024", "\\\\025", "\\\\026", "\\\\027", "\\\\030", "\\\\031", "\\\\032", "\\\\033", "\\\\034", "\\\\035",
+      "\\\\036", "\\\\037", " ",       "!",       "\\\"",    "#",       "$",       "%",       "&",       "\\\'",
+      "(",       ")",       "*",       "+",       ",",       "-",       ".",       "/",       "0",       "1",
+      "2",       "3",       "4",       "5",       "6",       "7",       "8",       "9",       ":",       ";",
+      "<",       "=",       ">",       "\\\?",    "@",       "A",       "B",       "C",       "D",       "E",
+      "F",       "G",       "H",       "I",       "J",       "K",       "L",       "M",       "N",       "O",
+      "P",       "Q",       "R",       "S",       "T",       "U",       "V",       "W",       "X",       "Y",
+      "Z",       "[",       "\\\\",    "]",       "^",       "_",       "`",       "a",       "b",       "c",
+      "d",       "e",       "f",       "g",       "h",       "i",       "j",       "k",       "l",       "m",
+      "n",       "o",       "p",       "q",       "r",       "s",       "t",       "u",       "v",       "w",
+      "x",       "y",       "z",       "{",       "|",       "}",       "~",       "\\\\177", "\\\\200", "\\\\201",
+      "\\\\202", "\\\\203", "\\\\204", "\\\\205", "\\\\206", "\\\\207", "\\\\210", "\\\\211", "\\\\212", "\\\\213",
+      "\\\\214", "\\\\215", "\\\\216", "\\\\217", "\\\\220", "\\\\221", "\\\\222", "\\\\223", "\\\\224", "\\\\225",
+      "\\\\226", "\\\\227", "\\\\230", "\\\\231", "\\\\232", "\\\\233", "\\\\234", "\\\\235", "\\\\236", "\\\\237",
+      "\\\\240", "\\\\241", "\\\\242", "\\\\243", "\\\\244", "\\\\245", "\\\\246", "\\\\247", "\\\\250", "\\\\251",
+      "\\\\252", "\\\\253", "\\\\254", "\\\\255", "\\\\256", "\\\\257", "\\\\260", "\\\\261", "\\\\262", "\\\\263",
+      "\\\\264", "\\\\265", "\\\\266", "\\\\267", "\\\\270", "\\\\271", "\\\\272", "\\\\273", "\\\\274", "\\\\275",
+      "\\\\276", "\\\\277", "\\\\300", "\\\\301", "\\\\302", "\\\\303", "\\\\304", "\\\\305", "\\\\306", "\\\\307",
+      "\\\\310", "\\\\311", "\\\\312", "\\\\313", "\\\\314", "\\\\315", "\\\\316", "\\\\317", "\\\\320", "\\\\321",
+      "\\\\322", "\\\\323", "\\\\324", "\\\\325", "\\\\326", "\\\\327", "\\\\330", "\\\\331", "\\\\332", "\\\\333",
+      "\\\\334", "\\\\335", "\\\\336", "\\\\337", "\\\\340", "\\\\341", "\\\\342", "\\\\343", "\\\\344", "\\\\345",
+      "\\\\346", "\\\\347", "\\\\350", "\\\\351", "\\\\352", "\\\\353", "\\\\354", "\\\\355", "\\\\356", "\\\\357",
+      "\\\\360", "\\\\361", "\\\\362", "\\\\363", "\\\\364", "\\\\365", "\\\\366", "\\\\367", "\\\\370", "\\\\371",
+      "\\\\372", "\\\\373", "\\\\374", "\\\\375", "\\\\376", "\\\\377"};
 
   for (const char c : src) {
-    const std::size_t char_len = cpp_escaped_len(c);
-    if (char_len == 1) {
-      *itr++ = c;
-    } else if (char_len == 2) {
-      switch (c) {
-      case '\n':
-        *itr++ = '\\';
-        *itr++ = 'n';
-        break;
-      case '\r':
-        *itr++ = '\\';
-        *itr++ = 'r';
-        break;
-      case '\t':
-        *itr++ = '\\';
-        *itr++ = 't';
-        break;
-      case '\"':
-        *itr++ = '\\';
-        *itr++ = '\"';
-        break;
-      case '\'':
-        *itr++ = '\\';
-        *itr++ = '\'';
-        break;
-      case '\\':
-        *itr++ = '\\';
-        *itr++ = '\\';
-        break;
-      case '?':
-        *itr++ = '\\';
-        *itr++ = '?';
-        break;
-      default:
-        break;
-      }
-    } else {
-      *itr++ = '\\';
-      // NOLINTBEGIN(cppcoreguidelines-avoid-magic-numbers,readability-magic-numbers)
-      *itr++ = static_cast<char>('0' + (static_cast<unsigned char>(c) / 64));
-      *itr++ = static_cast<char>('0' + ((static_cast<unsigned char>(c) % 64) / 8));
-      *itr++ = static_cast<char>('0' + (static_cast<unsigned char>(c) % 8));
-      // NOLINTEND(cppcoreguidelines-avoid-magic-numbers,readability-magic-numbers)
-    }
+    result += escapedChars[static_cast<unsigned char>(c)];
   }
   return result;
 }