expr.cxx

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//}}}
//{{{  next_token()                     

// ----------------------------------------------------------------------------
// Work out what the next token is. This includes the handling of
// strings, integers, doubles, and references.
static void
next_token()
{
    CYG_REPORT_FUNCNAMETYPE("next_token", "token %d");

    // Make sure there is no dross left lying around from the previous call.
    current_token       = T_Invalid;
    current_string      = "";
    current_reference   = "";
    current_int         = 0;
    current_double      = 0.0;
    current_format      = CdlValueFormat_Default;

    // Skip leading white space. This includes newlines, tabs, etc,
    // consider the case of:
    //    ...
    //    legal_values {
    //        1
    //        2
    //        4
    //        ..
    //    }
    //    ...
    // which is perfectly legitimate. White space inside strings
    // is handled by the string literal code, and does not get filtered
    // out here.
    //
    // Exactly which characters are white-space is implementation-defined,
    // so a special check for EOF is in order.
    while ((EOF != current_char) && isspace(current_char)) {
        next_char();
    }

    // Remember the token starting point. next_char() has actually moved
    // the index on by one.
    token_start = current_index - 1;

    // The simple cases can be handled inline, the more complicated cases
    // involve other functions
    switch(current_char) {

      case EOF:
          current_token = T_EOD;
          break;

      case '"':
          process_string();
          break;

      case '(':
          current_token = T_OpenBracket;
          next_char();
          break;

      case ')':
          current_token = T_CloseBracket;
          next_char();
          break;

          // At this level it is not possible to distinguish between
          // unary and binary operators, so no attempt is made to
          // turn - and + into part of a number.
      case '-':
          current_token = T_Minus;
          next_char();
          break;

      case '+':
          current_token = T_Plus;
          next_char();
          break;

      case '*':
          current_token = T_Times;
          next_char();
          break;

      case '/':
          current_token = T_Divide;
          next_char();
          break;

      case '!':
          next_char();
          if ('=' == current_char) {
              current_token = T_NotEqual;
              next_char();
          } else {
              current_token = T_Exclamation;
          }
          break;

      case '~':
          current_token = T_Tilde;
          next_char();
          break;

      case '?':
          current_token = T_Questionmark;
          next_char();
          break;

      case '%':
          current_token = T_Remainder;
          next_char();
          break;

      case '<':
          next_char();
          if ('<' == current_char) {
              current_token = T_LeftShift;
              next_char();
          } else if ('=' == current_char) {
              current_token = T_LessEqual;
              next_char();
          } else {
              current_token = T_LessThan;
          }
          break;

      case '>':
          next_char();
          if ('>' == current_char) {
              current_token = T_RightShift;
              next_char();
          } else if ('=' == current_char) {
              current_token = T_GreaterEqual;
              next_char();
          } else {
              current_token = T_GreaterThan;
          }
          break;

      case '=':
          next_char();
          if ('=' != current_char) {
              throw CdlParseException(std::string("Incomplete == operator in expression.\n") + get_error_location());
          } else {
              current_token = T_Equal;
              next_char();
          }
          break;

      case '&':
          next_char();
          if ('&' == current_char) {
              current_token = T_And;
              next_char();
          } else {
              current_token = T_BitAnd;
          }
          break;

      case '^':
          current_token = T_BitXor;
          next_char();
          break;

      case '|':
          next_char();
          if ('|' == current_char) {
              current_token = T_Or;
              next_char();
          } else {
              current_token = T_BitOr;
          }
          break;

      case ':':
          current_token = T_Colon;
          next_char();
          break;

      default:
          // String constants have been handled already. The only
          // valid tokens that are left are numbers, references and
          // the rang eoperator.
          //
          // Numbers should begin with a digit (plus and minus are
          // tokenized separately).
          //
          // References must be valid C preprocessor symbols, i.e.
          // they must begin with either a letter or an underscore.
          // The range operator is handled most conveniently as
          // a special case of a reference.
          if (isdigit(current_char)) {
              process_number();
          } else if (('_' == current_char) ||
                     (('a' <= current_char) && (current_char <= 'z')) ||
                     (('A' <= current_char) && (current_char <= 'Z'))) {
              process_reference();
              if ("to" == current_reference) {
                  current_reference = "";
                  current_token  = T_Range;
              } else {
                  current_token = T_Reference;
              }
          } else {
              std::string msg = "Unexpected character '";
              msg += (char) current_char;
              msg += "' in expression.\n";
              msg += get_error_location();
              throw CdlParseException(msg);
          }
          break;
    }

    CYG_REPORT_RETVAL(current_token);
}

//}}}
//{{{  initialise_tokenisation()        

// ----------------------------------------------------------------------------
// This is called at the start of expression parsing. It
// sets up the appropriate statics, and provides initial
// values for current_char and current_token.
static void
initialise_tokenisation(std::string data, int index)
{
    CYG_REPORT_FUNCNAME("initialise_tokenization");

    current_data        = data;
    current_index       = static_cast<unsigned int>(index);
    token_start         = current_index;
    next_char();
    next_token();

    CYG_REPORT_RETURN();
}

//}}}

//}}}
//{{{  Syntactic analysis               

// ----------------------------------------------------------------------------
// Syntactic analysis.
//
// The BNF of CDL expressions is something like this:
//
//   <expression>   ::= <conditional>
//   <conditional>  ::= <or> ? <conditional> : <conditional> | <or>
//   <or>           ::= <and>    [<or op>     <and>]           ||
//   <and>          ::= <bitor>  [<and op>    <bitor>]         ??
//   <bitor>        ::= <bitxor> [<bitor op>  <bitxor>]        |
//   <bitxor>       ::= <bitand> [<bitxor op> <bitand>]        ^
//   <bitand>       ::= <eq>     [<bitand op> <eq>]            &
//   <eq>           ::= <comp>   [<eq op>     <comp>]          == !=
//   <comp>         ::= <shift>  [<comp op>   <shift>]         < <= > >=
//   <shift>        ::= <add>    [<shift op>  <add>]           << >>
//   <add>          ::= <mult>   [<add op>    <mult>]          + -
//   <mult>         ::= <unary>  [<mult op>   <unary>]         * / %
//   <unary>        ::= -<unary> | +<unary> | !<unary> | *<unary> | ?<unary> |
//                      ~<unary> |
//                      <string constant> | <integer constant> |
//                      <double constant> | <reference> |
//                      ( <expression> )
//
// There are separate functions for each of these terms.

// A forward declaration, needed for bracketed subexpressions.
static void parse_expression(CdlExpression);

// A utility to add a reference to the current expression, returning
// the index.
static int
push_reference(CdlExpression expr, const std::string& reference)
{
    CYG_REPORT_FUNCNAMETYPE("push_reference", "new index %d");
    CYG_PRECONDITION_CLASSC(expr);

    CdlReference ref(reference);
    expr->references.push_back(ref);
    int result = (int) expr->references.size() - 1;

    CYG_REPORT_RETVAL(result);
    return result;
}

// A utility to add a subexpression, returning its index.
static void
push_subexpression(CdlExpression expr, const CdlSubexpression& subexpr)
{
    CYG_REPORT_FUNCNAME("push_subexpression");
    CYG_PRECONDITION_CLASSC(expr);

    expr->sub_expressions.push_back(subexpr);
    expr->first_subexpression = ((int) expr->sub_expressions.size()) - 1;

    CYG_REPORT_RETURN();
}

// Another utility to hold of the most recent subexpression
static CdlSubexpression&
current_subexpression(CdlExpression expr)
{
    CYG_REPORT_FUNCNAME("current_subexpression");

    CdlSubexpression& result = expr->sub_expressions[expr->first_subexpression];

    CYG_REPORT_RETURN();
    return result;
}

static void
parse_unary(CdlExpression expr)
{
    CYG_REPORT_FUNCNAME("parse_operand");
    CYG_REPORT_FUNCARG1XV(expr);
    CYG_PRECONDITION_CLASSC(expr);

    CdlSubexpression subexpr;

    switch(current_token) {
      case T_EOD :
      {
        // This warrants a special case
        throw CdlParseException("End of expression reached when expecting an operand.\n" + get_error_location());
      }
      
      case T_Reference :
      {
        subexpr.op              = CdlExprOp_Reference;
        subexpr.reference_index = push_reference(expr, current_reference);
        push_subexpression(expr, subexpr);
        next_token();
        break;
      }
      
      case T_String :
      {
        subexpr.op              = CdlExprOp_StringConstant;
        subexpr.constants       = current_string;
        push_subexpression(expr, subexpr);
        next_token();
        break;
      }
      
      case T_Integer :
      {
        subexpr.op               = CdlExprOp_IntegerConstant;
        subexpr.constants.set_integer_value(current_int, current_format);
        push_subexpression(expr, subexpr);
        next_token();
        break;
      }
      
      case T_Double :
      {
        subexpr.op              = CdlExprOp_DoubleConstant;
        subexpr.constants.set_double_value(current_double, current_format);
        push_subexpression(expr, subexpr);
        next_token();
        break;
      }
      
      case T_OpenBracket :
      {
        next_token();
        parse_expression(expr);
        if (T_CloseBracket != current_token) {
            throw CdlParseException("Missing close bracket after subexpression.\n" + get_error_location());
        }
        next_token();
        break;
      }
      
      case T_Minus :
      {
        next_token();