Code-review fixes 2

Author: TheStormN

Diff for: src/lib_json/json_writer.cpp

@@ -309,28 +309,26 @@ static String valueToQuotedStringN(const char* value, unsigned length,
     // Should add a flag to allow this compatibility mode and prevent this
     // sequence from occurring.
     default: {
-      unsigned int codepoint =
-          emitUTF8 ? static_cast<unsigned char>(*c) : utf8ToCodepoint(c, end);
-      const unsigned int FIRST_NON_CONTROL_CODEPOINT = 0x20;
-      const unsigned int LAST_NON_CONTROL_CODEPOINT = 0x7F;
-      const unsigned int FIRST_SURROGATE_PAIR_CODEPOINT = 0x10000;
-
-      if ((codepoint < FIRST_NON_CONTROL_CODEPOINT) ||
-          (!emitUTF8 && (codepoint >= LAST_NON_CONTROL_CODEPOINT))) {
-        auto appendHexChar = [&result](unsigned ch) {
-          result.append("\\u").append(toHex16Bit(ch));
-        };
-        if (codepoint < FIRST_SURROGATE_PAIR_CODEPOINT) {
+      const auto appendHexChar = [&result](unsigned ch) {
+        result.append("\\u").append(toHex16Bit(ch));
+      };
+
+      unsigned codepoint = static_cast<unsigned>(*c);
+      if (codepoint > 0x7F && !emitUTF8) {
+        codepoint = utf8ToCodepoint(c, end);
+        if (codepoint < 0x10000) {
           // codepoint is in Basic Multilingual Plane
           appendHexChar(codepoint);
         } else {
           // codepoint is not in Basic Multilingual Plane
-          codepoint -= FIRST_SURROGATE_PAIR_CODEPOINT;
+          codepoint -= 0x10000;
           appendHexChar(0xD800 + (codepoint >> 10));
           appendHexChar(0xDC00 + (codepoint & 0x3FF));
         }
+      } else if (codepoint < 0x20) {
+        appendHexChar(codepoint);
       } else {
-        result += *c;
+        result += static_cast<char>(codepoint);
       }
     } break;
     }