Method parseEscape

java/com/google/re2j/Parser.java:1336–1450

(StringIterator t)

  // and returns the rune.
  // Pre: t at '\\'.  Post: after escape.
  @SuppressWarnings("fallthrough") // disables *all* fallthru checking. Lame.
  private static int parseEscape(StringIterator t) throws PatternSyntaxException {
    int startPos = t.pos();
    t.skip(1); // '\\'
    if (!t.more()) {
      throw new PatternSyntaxException(ERR_TRAILING_BACKSLASH);
    }
    int c = t.pop();
    bigswitch:
    switch (c) {
      default:
        if (!Utils.isalnum(c)) {
          // Escaped non-word characters are always themselves.
          // PCRE is not quite so rigorous: it accepts things like
          // \q, but we don't.  We once rejected \_, but too many
          // programs and people insist on using it, so allow \_.
          return c;
        }
        break;

        // Octal escapes.
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
        // Single non-zero digit is a backreference; not supported
        if (!t.more() || t.peek() < '0' || t.peek() > '7') {
          break;
        }
        /* fallthrough */
      case '0':
        // Consume up to three octal digits; already have one.
        int r = c - '0';
        for (int i = 1; i < 3; i++) {
          if (!t.more() || t.peek() < '0' || t.peek() > '7') {
            break;
          }
          r = r * 8 + t.peek() - '0';
          t.skip(1); // digit
        }
        return r;

        // Hexadecimal escapes.
      case 'x':
        if (!t.more()) {
          break;
        }
        c = t.pop();
        if (c == '{') {
          // Any number of digits in braces.
          // Perl accepts any text at all; it ignores all text
          // after the first non-hex digit.  We require only hex digits,
          // and at least one.
          int nhex = 0;
          r = 0;