int UnescapeCEscapeSequences()

in cdk/extra/protobuf/protobuf-3.19.6/src/google/protobuf/stubs/strutil.cc [314:432]
111 lines of code
41 McCabe index (conditional complexity)

int UnescapeCEscapeSequences(const char *source, char *dest,
                             std::vector<std::string> *errors) {
  GOOGLE_DCHECK(errors == nullptr) << "Error reporting not implemented.";

  char* d = dest;
  const char* p = source;

  // Small optimization for case where source = dest and there's no escaping
  while ( p == d && *p != '\0' && *p != '\\' )
    p++, d++;

  while (*p != '\0') {
    if (*p != '\\') {
      *d++ = *p++;
    } else {
      switch ( *++p ) {                    // skip past the '\\'
        case '\0':
          LOG_STRING(ERROR, errors) << "String cannot end with \\";
          *d = '\0';
          return d - dest;   // we're done with p
        case 'a':  *d++ = '\a';  break;
        case 'b':  *d++ = '\b';  break;
        case 'f':  *d++ = '\f';  break;
        case 'n':  *d++ = '\n';  break;
        case 'r':  *d++ = '\r';  break;
        case 't':  *d++ = '\t';  break;
        case 'v':  *d++ = '\v';  break;
        case '\\': *d++ = '\\';  break;
        case '?':  *d++ = '\?';  break;    // \?  Who knew?
        case '\'': *d++ = '\'';  break;
        case '"':  *d++ = '\"';  break;
        case '0': case '1': case '2': case '3':  // octal digit: 1 to 3 digits
        case '4': case '5': case '6': case '7': {
          char ch = *p - '0';
          if ( IS_OCTAL_DIGIT(p[1]) )
            ch = ch * 8 + *++p - '0';
          if ( IS_OCTAL_DIGIT(p[1]) )      // safe (and easy) to do this twice
            ch = ch * 8 + *++p - '0';      // now points at last digit
          *d++ = ch;
          break;
        }
        case 'x': case 'X': {
          if (!isxdigit(p[1])) {
            if (p[1] == '\0') {
              LOG_STRING(ERROR, errors) << "String cannot end with \\x";
            } else {
              LOG_STRING(ERROR, errors) <<
                "\\x cannot be followed by non-hex digit: \\" << *p << p[1];
            }
            break;
          }
          unsigned int ch = 0;
          const char *hex_start = p;
          while (isxdigit(p[1]))  // arbitrarily many hex digits
            ch = (ch << 4) + hex_digit_to_int(*++p);
          if (ch > 0xFF)
            LOG_STRING(ERROR, errors)
                << "Value of "
                << "\\" << std::string(hex_start, p + 1 - hex_start)
                << " exceeds 8 bits";
          *d++ = ch;
          break;
        }
#if 0  // TODO(kenton):  Support \u and \U?  Requires runetochar().
        case 'u': {
          // \uhhhh => convert 4 hex digits to UTF-8
          char32 rune = 0;
          const char *hex_start = p;
          for (int i = 0; i < 4; ++i) {
            if (isxdigit(p[1])) {  // Look one char ahead.
              rune = (rune << 4) + hex_digit_to_int(*++p);  // Advance p.
            } else {
              LOG_STRING(ERROR, errors)
                << "\\u must be followed by 4 hex digits: \\"
                <<  std::string(hex_start, p+1-hex_start);
              break;
            }
          }
          d += runetochar(d, &rune);
          break;
        }
        case 'U': {
          // \Uhhhhhhhh => convert 8 hex digits to UTF-8
          char32 rune = 0;
          const char *hex_start = p;
          for (int i = 0; i < 8; ++i) {
            if (isxdigit(p[1])) {  // Look one char ahead.
              // Don't change rune until we're sure this
              // is within the Unicode limit, but do advance p.
              char32 newrune = (rune << 4) + hex_digit_to_int(*++p);
              if (newrune > 0x10FFFF) {
                LOG_STRING(ERROR, errors)
                  << "Value of \\"
                  << std::string(hex_start, p + 1 - hex_start)
                  << " exceeds Unicode limit (0x10FFFF)";
                break;
              } else {
                rune = newrune;
              }
            } else {
              LOG_STRING(ERROR, errors)
                << "\\U must be followed by 8 hex digits: \\"
                <<  std::string(hex_start, p+1-hex_start);
              break;
            }
          }
          d += runetochar(d, &rune);
          break;
        }
#endif
        default:
          LOG_STRING(ERROR, errors) << "Unknown escape sequence: \\" << *p;
      }
      p++;                                 // read past letter we escaped
    }
  }
  *d = '\0';
  return d - dest;
}