this needs to be fast

/**
  @section Implementation

  For the preprocessor's implementation, we switch gears a bit. The preprocessor needs
  to be the fastest aspect of the entire parser, as directives are everywhere. As such,
  it operates on a hacked-up switch statement using a whole heap of gotos, designed to
  support a specific set of macros. Inserting a new directive into this switch is still
  simple enough, but unlike other aspects of the parser, is not as trivial as a single
  function call. Don't gripe; originally I was going to use a perfect hash.
**/
void lexer_cpp::handle_preprocessor() {
  while (cfile[pos] == ' ' or cfile[pos] == '\t') ++pos;
  switch (cfile[pos++])
  {
    case 'd':
      if (strbw(cfile+pos, "efine")) { pos += 5; goto case_define; }
      goto failout;
      case 'e':
      if (cfile[pos] == 'n') { if (strbw(cfile+pos+1, "dif")) { pos += 4; goto case_endif; } goto failout; }
      if (cfile[pos] == 'l')
      {
        if (cfile[++pos] == 's') { if (cfile[++pos] == 'e') { ++pos; goto case_else; } goto failout; }
        if (cfile[pos] == 'i' and cfile[++pos] == 'f')
        {
          if (strbw(cfile[++pos])) goto case_elif;
          if (cfile[pos] == 'd') { if (strbw(cfile+pos+1, "ef"))  { pos += 3; goto case_elifdef;  } goto failout; }
          if (cfile[pos] == 'n') { if (strbw(cfile+pos+1, "def")) { pos += 4; goto case_elifndef; } goto failout; }
        }
        goto failout;
      }
      if (strbw(cfile+pos, "rror")) { pos += 4; goto case_error; }
      goto failout;
      case 'i':
      if (cfile[pos] == 'f')
      {
        if (strbw(cfile[++pos])) goto case_if;
        if (cfile[pos] == 'd') { if (strbw(cfile+pos+1, "ef"))  { pos += 3; goto case_ifdef;  } goto failout; }
        if (cfile[pos] == 'n') { if (strbw(cfile+pos+1, "def")) { pos += 4; goto case_ifndef; } goto failout; }
        goto failout;
      }
      if (cfile[pos] == 'n') { if (strbw(cfile+pos+1, "clude")) { pos += 6; goto case_include; } goto failout; }
      if (cfile[pos] == 'm') { if (strbw(cfile+pos+1, "port"))  { pos += 5; goto case_import;  } goto failout; }
      goto failout;
      case 'l':
      if (strbw(cfile+pos, "ine")) { pos += 3; goto case_line; }
      goto failout;
      case 'p':
      if (strbw(cfile+pos, "ragma")) { pos += 5; goto case_pragma; }
      goto failout;
      case 'u':
      if (strbw(cfile+pos, "ndef")) { pos += 4; goto case_undef; }
      if (strbw(cfile+pos, "sing")) { pos += 4; goto case_using; }
      goto failout;
    case 'w':
      if (strbw(cfile+pos, "arning")) { pos += 7; goto case_warning; }
      goto failout;
    default: goto failout;