A2OS/source/FoxAssembler.Mod

MODULE FoxAssembler;   (**  AUTHOR "fof"; PURPOSE "Oberon Assembler: Generic Part";  **)
(* (c) fof ETH Zürich, 2009 *)

IMPORT Streams, Strings, Diagnostics,D := Debugging, Commands, BinaryCode := FoxBinaryCode, SyntaxTree := FoxSyntaxTree, Global := FoxGlobal,
	IntermediateCode := FoxIntermediateCode, Sections := FoxSections, Scanner := FoxScanner, Basic := FoxBasic, SYSTEM, ObjectFile;

CONST
	Trace* = FALSE;   (* debugging output *)

	MaxOperands* = 3;

	(*
		currently there is conceptual support for one-pass assembly with a fixup mechanism for section-local references
		disadvantages of one-pass assembly:
			- expressions with labels would not work
			- fixup mechanism complicated and not generic

	*)
	MaxPasses* = 2;

	ConstantInteger* = 0;
	ConstantFloat* = 1;
	Fixup* = 2;
	Offset* = 3;
	ConstantIntegerOrOffset* = {ConstantInteger, Offset};

TYPE
	OperandString=ARRAY 256 OF CHAR;
	Position= Basic.Position;

	FixupElement=POINTER TO RECORD
		fixup: BinaryCode.Fixup; next: FixupElement;
	END;

	NamedLabel*= OBJECT
	VAR
		section: IntermediateCode.Section;
		offset, displacement: LONGINT; (* in contrast to offset, displacement will be reset each round of assembling. This is to make sure that GetFixup generates the right displacement in the fixup *)
		name-: Scanner.IdentifierString;
		nextNamedLabel-: NamedLabel;
		fixupList: FixupElement;

		PROCEDURE &InitNamedLabel(section: IntermediateCode.Section; CONST name: ARRAY OF CHAR);
		BEGIN
			fixupList := NIL;
			SELF.offset := 0; (* must be zero to be able to track local displacement *)
			SELF.section := section;
			COPY(name,SELF.name);
			nextNamedLabel := NIL;
		END InitNamedLabel;

		PROCEDURE GetFixup(): BinaryCode.Fixup;
		VAR fixup: BinaryCode.Fixup; element: FixupElement; identifier: ObjectFile.Identifier;
		BEGIN
			identifier.name := section.name;
			fixup := BinaryCode.NewFixup(BinaryCode.Absolute,0,identifier,0,displacement,0,NIL);
			NEW(element); element.fixup := fixup; element.next := fixupList; fixupList := element;
			RETURN fixup;
		END GetFixup;

		PROCEDURE ResetDisplacements;
		VAR element: FixupElement;
		BEGIN
			displacement := 0;
			element := fixupList;
			WHILE element # NIL DO
				element.fixup.SetSymbol(section.name,0,0,0);
				element := element.next;
			END;
		END ResetDisplacements;

		PROCEDURE SetOffset*(ofs: LONGINT);
		VAR element: FixupElement;
		BEGIN
			SELF.offset := ofs;
			displacement := ofs;
			element := fixupList;
			WHILE element # NIL DO
				element.fixup.SetSymbol(section.name,0,0,element.fixup.displacement (* must be here to take into account modifications of code emission *) +displacement);
				element := element.next;
			END;
		END SetOffset;

	END NamedLabel;

	NamedLabelList*=OBJECT
	VAR first-,last-: NamedLabel;

		PROCEDURE & InitNamedLabelList;
		BEGIN first := NIL; last := NIL
		END InitNamedLabelList;

		PROCEDURE Add*(n: NamedLabel);
		BEGIN
			IF first = NIL THEN first := n ELSE last.nextNamedLabel := n; last.nextNamedLabel := n;  END; last := n;
		END Add;

		PROCEDURE ResetDisplacements;
		VAR label: NamedLabel;
		BEGIN
			label := first;
			WHILE label # NIL DO label.ResetDisplacements; label := label.nextNamedLabel END;
		END ResetDisplacements;

		PROCEDURE Find*(CONST name: ARRAY OF CHAR): NamedLabel;
		VAR label: NamedLabel;
		BEGIN
			label := first;
			WHILE (label # NIL) & (label.name # name)  DO
				label := label.nextNamedLabel;
			END;
			RETURN label
		END Find;

	END NamedLabelList;

	Result*= RECORD
		type*: INTEGER; (* ConstantInteger, ConstantFloat, Fixup, Offset *)
		sizeInBits*: INTEGER;
		value*: HUGEINT;
		valueR*: LONGREAL;
		fixup*: BinaryCode.Fixup;
	END;

	NamedResult*=POINTER TO RECORD (Result)
		name: Scanner.IdentifierString;
		nextResult: NamedResult;
	END;

	NamedResultList*=OBJECT
	VAR first, last: NamedResult; number: LONGINT;

		PROCEDURE & InitNamedResultList;
		BEGIN first := NIL; last := NIL; number := 0;
		END InitNamedResultList;

		PROCEDURE Add*(n: NamedResult);
		BEGIN
			IF first = NIL THEN first := n ELSE last.nextResult := n END; last := n; INC(number);
		END Add;

		PROCEDURE Find*(CONST name: ARRAY OF CHAR): NamedResult;
		VAR result: NamedResult;
		BEGIN
			result := first;
			WHILE (result # NIL) & (result.name # name)  DO
				result := result.nextResult;
			END;
			RETURN result
		END Find;

	END NamedResultList;

	Assembler*= OBJECT
	VAR
		diagnostics: Diagnostics.Diagnostics;
		error-: BOOLEAN;
		errorPosition-: Position;
		token-: Scanner.Token;
		scanner: Scanner.AssemblerScanner;
		orgOffset: LONGINT;
		section-: IntermediateCode.Section;
		code-: BinaryCode.Section;
		labels: NamedLabelList;
		results: NamedResultList;
		scope: SyntaxTree.Scope;
		module: Sections.Module;
		pass-: LONGINT;

		PROCEDURE &Init*(diagnostics: Diagnostics.Diagnostics);
		BEGIN
			SELF.diagnostics := diagnostics; errorPosition := Basic.invalidPosition; orgOffset := 0;
		END Init;

		PROCEDURE SetContext(CONST context: Scanner.Context);
		BEGIN
			scanner.SetContext(context); NextToken;
		END SetContext;

		PROCEDURE Error*(pos: SyntaxTree.Position; CONST msg: ARRAY OF CHAR);
		BEGIN
			error := TRUE;
			Basic.Error(diagnostics, scanner.source^,pos, msg);
		END Error;

		PROCEDURE ErrorSS*(pos: SyntaxTree.Position; CONST s1,s2: ARRAY OF CHAR);
		VAR msg: Basic.MessageString;
		BEGIN COPY(s1,msg); Strings.Append(msg,s2); Error(pos, msg);
		END ErrorSS;

		PROCEDURE NextToken*;
		BEGIN error := error OR ~scanner.GetNextToken(token); errorPosition := token.position;
		END NextToken;

		PROCEDURE ThisSymbol*(x: Scanner.Symbol): BOOLEAN;
		BEGIN
			IF ~error & (token.symbol = x) THEN NextToken; RETURN TRUE ELSE RETURN FALSE END;
		END ThisSymbol;

		PROCEDURE GetIdentifier*(VAR pos: Position; VAR identifier: ARRAY OF CHAR): BOOLEAN;
		BEGIN
			pos := token.position;
			IF token.symbol # Scanner.Identifier THEN RETURN FALSE
			ELSE COPY(token.identifierString,identifier); NextToken; RETURN TRUE
			END;
		END GetIdentifier;

		PROCEDURE ThisIdentifier*(CONST this: ARRAY OF CHAR): BOOLEAN;
		BEGIN
			IF ~error & (token.symbol = Scanner.Identifier) & (this = token.identifierString) THEN NextToken; RETURN TRUE ELSE RETURN FALSE END;
		END ThisIdentifier;

		PROCEDURE ExpectIdentifier*(VAR pos: Position; VAR identifier: ARRAY OF CHAR): BOOLEAN;
		BEGIN
			IF ~GetIdentifier(pos,identifier)THEN Error(errorPosition,"identifier expected"); RETURN FALSE
			ELSE RETURN TRUE
			END;
		END ExpectIdentifier;

		PROCEDURE ExpectSymbol*(x: Scanner.Symbol): BOOLEAN;
		VAR s: Basic.MessageString;
		BEGIN
			IF ThisSymbol(x) THEN RETURN TRUE
			ELSE
				s := "expected token "; Strings.Append(s,Scanner.symbols[x]); Strings.Append(s," but got "); Strings.Append(s,Scanner.symbols[token.symbol]);
				Error(errorPosition,s);RETURN FALSE
			END;
		END ExpectSymbol;

		PROCEDURE ExpectConstantInteger*(VAR x: Result; critical: BOOLEAN): BOOLEAN;
		VAR result: Result;
		BEGIN
			IF ~Expression(result,critical) OR (result.type # ConstantInteger) THEN
				result.value := 0;
				IF critical THEN Error(errorPosition,"constant integer expected") END;
				RETURN ~critical
			ELSE RETURN TRUE
			END
		END ExpectConstantInteger;

		PROCEDURE Section;
		VAR sectionType: Scanner.IdentifierString; pos: Position;
		BEGIN
			IF ExpectSymbol(Scanner.Period) THEN
				IF ExpectIdentifier(pos,sectionType) THEN
					IF sectionType = "data" THEN
						IF Trace THEN D.String("data section"); D.Ln END;
						(*! generate section here, if allowed *)
					ELSIF sectionType = "code" THEN
						IF Trace THEN D.String("code section"); D.Ln END;
						(*! generate section here, if allowed *)
					ELSE Error(pos,"expected data or code");
					END;
				END;
			END;
		END Section;

		PROCEDURE DefineLabel(pos: Position; CONST name: ARRAY OF CHAR);
		VAR label: NamedLabel;
		BEGIN
			IF Trace THEN D.String("define label: "); D.String(name); D.Ln END;
			IF labels.Find(name) # NIL THEN
				Error(pos,"multiply declared identifier")
			ELSE
				NEW(label,section,name);
				labels.Add(label);
				ASSERT(labels.Find(name) =label);
			END;
		END DefineLabel;

		PROCEDURE SetLabel(pos: Position; CONST name: ARRAY OF CHAR);
		VAR label: NamedLabel;
		BEGIN
			IF Trace THEN D.String("set label: "); D.String(name); D.String(" "); D.Int(code.pc,1); D.Ln END;
			label := labels.Find(name);
			label.SetOffset(code.pc);
		END SetLabel;

		PROCEDURE CopyResult(CONST from: Result; VAR to: Result);
		BEGIN
			to.type := from.type;
			to.sizeInBits := from.sizeInBits;
			to.value := from.value;
			to.valueR := from.valueR;
			to.fixup := from.fixup;
		END CopyResult;

		PROCEDURE DefineResult(pos: Position; CONST name: ARRAY OF CHAR; CONST r: Result);
		VAR result: NamedResult;
		BEGIN
			IF Trace THEN D.String("define result: "); D.String(name); D.Ln END;
			IF results.Find(name) # NIL THEN
				Error(pos,"multiply declared identifier")
			ELSE
				NEW(result); COPY(name,result.name);
				CopyResult(r,result^);
				results.Add(result);
				ASSERT(results.Find(name) =result);
			END;
		END DefineResult;

		PROCEDURE SetResult(CONST name: ARRAY OF CHAR; CONST r: Result);
		VAR result: NamedResult;
		BEGIN
			IF Trace THEN D.String("define result: "); D.String(name); D.Ln END;
			result := results.Find(name);
			CopyResult(r,result^);
		END SetResult;

		PROCEDURE SymbolInScope(CONST ident: ARRAY OF CHAR): SyntaxTree.Symbol;
		VAR sym: SyntaxTree.Symbol; localScope: SyntaxTree.Scope;  identifier: SyntaxTree.Identifier;
		CONST Trace=FALSE;
		BEGIN
			IF scope = NIL THEN RETURN NIL END;
			localScope := scope;
			identifier := SyntaxTree.NewIdentifier(ident);
			IF Trace THEN D.String("GetScopeSymbol:"); D.String(ident); D.Ln; END;
			WHILE (sym = NIL) & (localScope # NIL) DO
				sym := localScope.FindSymbol(identifier);
				localScope := localScope.outerScope
			END;

			IF (sym # NIL) & (sym IS SyntaxTree.Import)  THEN
				NextToken;
				IF ExpectSymbol(Scanner.Period) & (token.symbol = Scanner.Identifier) THEN
					identifier := SyntaxTree.NewIdentifier(token.identifierString);
					IF Trace THEN D.String("GetScopeSymbol  :"); D.String(token.identifierString); D.Ln; END;
					localScope := sym(SyntaxTree.Import).module.moduleScope;
					sym := NIL;
					WHILE (sym = NIL) & (localScope # NIL) DO
						sym := localScope.FindSymbol(identifier);
						IF (sym # NIL) & (sym.access * SyntaxTree.Public = {}) THEN sym := NIL END;
						localScope := localScope.outerScope
					END;
				ELSE RETURN NIL
				END;
			END;
			IF Trace THEN IF sym = NIL THEN D.String("not found") ELSE D.String("found"); END; D.Ln; END;
			RETURN sym
		END SymbolInScope;

		PROCEDURE ConstantSymbol(pos: Position; constant: SyntaxTree.Constant; VAR result: Result): BOOLEAN;
		BEGIN
			IF constant.type.resolved IS SyntaxTree.CharacterType THEN
				result.value := ORD(constant.value.resolved(SyntaxTree.CharacterValue).value);
				result.valueR := result.value;
				result.type := ConstantInteger;
			ELSIF constant.type.resolved IS SyntaxTree.IntegerType THEN
				result.value := constant.value.resolved(SyntaxTree.IntegerValue).value;
				result.valueR := result.value;
				result.type := ConstantInteger;
			ELSIF constant.type.resolved IS SyntaxTree.FloatType THEN
				result.valueR := constant.value.resolved(SyntaxTree.RealValue).value;
				result.type := ConstantFloat;
			ELSE
				Error(pos,"incompatible constant");
				RETURN FALSE;
			END;
			result.sizeInBits := SHORT(module.system.SizeOf(constant.type));
			RETURN TRUE
		END ConstantSymbol;

		PROCEDURE GetFingerprint(symbol: SyntaxTree.Symbol): Basic.Fingerprint;
		BEGIN
			IF (symbol # NIL) THEN RETURN symbol.fingerprint.shallow END;
		END GetFingerprint;

		PROCEDURE NonConstantSymbol(pos: Position; symbol: SyntaxTree.Symbol; VAR result: Result): BOOLEAN;
		VAR
			name: Basic.SegmentedName; moduleScope: SyntaxTree.Scope; fixupSection: IntermediateCode.Section;
			fixupPatternList: ObjectFile.FixupPatterns; identifier: ObjectFile.Identifier;
		BEGIN
			IF scope = NIL THEN RETURN FALSE END;
			moduleScope := scope.ownerModule.moduleScope;
			Global.GetSymbolSegmentedName(symbol,name);
			identifier.name := name;
			identifier.fingerprint := GetFingerprint(symbol);

			IF symbol.scope IS SyntaxTree.ModuleScope THEN (* symbol in module scope *)
				IF symbol IS SyntaxTree.Variable THEN (* global variable *)
					result.type := Fixup;
					result.sizeInBits := SHORT(module.system.SizeOf(symbol.type));

					(* generic fixup pattern list for generic implementation of data instruction etc. -- otherwise replaced during encoding *)
					NEW(fixupPatternList, 1);
					fixupPatternList[0].bits := result.sizeInBits;
					fixupPatternList[0].offset := 0;
					result.fixup := BinaryCode.NewFixup(BinaryCode.Absolute, 0, identifier, 0, 0, 0, fixupPatternList);

				ELSIF symbol IS SyntaxTree.Procedure THEN (* procedure *)
					IF symbol(SyntaxTree.Procedure).isInline THEN
						Error(pos,"forbidden reference to inline procedure"); RETURN FALSE
					ELSE
						result.type := Fixup;
						result.sizeInBits := SHORT(module.system.SizeOf(symbol.type));
						(* generic fixup pattern list for generic implementation of data instruction etc. -- otherwise replaced during encoding *)
						NEW(fixupPatternList, 1);
						fixupPatternList[0].bits := result.sizeInBits;
						fixupPatternList[0].offset := 0;
						result.fixup := BinaryCode.NewFixup(BinaryCode.Absolute, 0, identifier, 0, 0, 0, fixupPatternList);
					END;
				ELSE HALT(100);
				END;
			ELSIF symbol.scope IS SyntaxTree.ProcedureScope THEN (* symbol in procedure (local) scope *)
				IF symbol.scope # scope THEN
					Error(pos,"local symbol not in current scope");
				ELSE
					RETURN FALSE;
					IF (symbol IS SyntaxTree.Variable) OR (symbol IS SyntaxTree.Parameter) THEN
						result.type := Offset;
						result.value := symbol.offsetInBits DIV module.system.dataUnit;
						ASSERT(symbol.offsetInBits MOD module.system.dataUnit = 0);
						result.sizeInBits := SHORT(module.system.SizeOf(symbol.type));
					ELSE Error(pos,"forbidden symbol in local scope");
					END;
				END
			ELSIF symbol.scope IS SyntaxTree.RecordScope THEN (* symbol in record scope *)
			ELSE Error(pos,"symbol in forbidden scope"); RETURN FALSE
			END;
			RETURN TRUE
		END NonConstantSymbol;

		PROCEDURE GetNonConstant*(pos: Position; CONST ident: ARRAY OF CHAR; VAR result: Result): BOOLEAN;
		VAR symbol: SyntaxTree.Symbol; namedLabel: NamedLabel;
			name: Basic.SegmentedName;fixupPatternList: ObjectFile.FixupPatterns;
			string: ARRAY 256 OF CHAR;
			identifier: ObjectFile.Identifier;
		BEGIN
			namedLabel := labels.Find(ident);
			IF (namedLabel # NIL) THEN
				result.type := Fixup;
				result.fixup := namedLabel.GetFixup();
				RETURN TRUE
			END;
			IF ident[0] = "@" THEN
				result.type := Fixup;
				COPY(ident, string);
				Strings.Delete(string,0,1);
				Basic.ToSegmentedName(string, name);
				result.sizeInBits := 32;
				NEW(fixupPatternList, 1);
				fixupPatternList[0].bits := result.sizeInBits;
				fixupPatternList[0].offset := 0;
				identifier.name := name;
				identifier.fingerprint := 0;
				result.fixup := BinaryCode.NewFixup(BinaryCode.Absolute, 0, identifier, 0, 0, 0, fixupPatternList);
				RETURN TRUE
			END;
			symbol := SymbolInScope(ident);
			IF symbol = NIL THEN RETURN FALSE
			ELSIF symbol IS SyntaxTree.Constant THEN RETURN FALSE
			ELSE RETURN NonConstantSymbol(pos,symbol,result)
			END;
		END GetNonConstant;

		PROCEDURE LocalOffset(pos: Position; symbol: SyntaxTree.Symbol; VAR result: Result): BOOLEAN;
		BEGIN
			IF symbol.scope IS SyntaxTree.ProcedureScope THEN (* symbol in procedure (local) scope *)
				IF symbol.scope = scope THEN
					IF (symbol IS SyntaxTree.Variable) OR (symbol IS SyntaxTree.Parameter) THEN
						result.type := ConstantInteger;
						result.value := symbol.offsetInBits DIV module.system.dataUnit;
						ASSERT(symbol.offsetInBits MOD module.system.dataUnit = 0);
						result.sizeInBits := SHORT(module.system.SizeOf(symbol.type));
						RETURN TRUE
					END;
				END;
			END;
			RETURN FALSE
		END LocalOffset;

		PROCEDURE GetConstant*(pos: Position; CONST ident: ARRAY OF CHAR; VAR result: Result): BOOLEAN;
		VAR symbol: SyntaxTree.Symbol; namedResult: NamedResult;
		BEGIN
			namedResult := results.Find(ident);
			IF namedResult # NIL THEN CopyResult(namedResult^,result); RETURN TRUE END;
			symbol := SymbolInScope(ident);
			IF symbol = NIL THEN RETURN FALSE
			ELSIF symbol IS SyntaxTree.Constant THEN RETURN ConstantSymbol(pos,symbol(SyntaxTree.Constant),result)
			ELSIF LocalOffset(pos,symbol,result) THEN RETURN TRUE
			ELSE RETURN FALSE
			END;
		END GetConstant;

		PROCEDURE Factor (VAR x: Result; critical: BOOLEAN): BOOLEAN;
		VAR label: NamedLabel; identifier: Scanner.IdentifierString; pos: Position;
		BEGIN
			IF ThisSymbol(Scanner.Number) THEN
				(* ASSERT(symbol.numberType = Scanner.Integer); *)
				IF token.numberType = Scanner.Integer THEN
					x.value := token.integer
				ELSIF token.numberType = Scanner.Hugeint THEN
					x.value := token.hugeint;
					(* ASSERT(x.value < 0); (* the resulting 32 bit integer must be negative when interpreted as a signed value *)*)
				END;
				x.type := ConstantInteger;
				RETURN TRUE;
			ELSIF ThisSymbol(Scanner.PC) THEN (* pc IN units ! *)
				x.value := code.pc;
				x.type := ConstantInteger; (* TODO: should it be 'x.type := Offset'? *)
				RETURN TRUE;
			ELSIF ThisSymbol(Scanner.PCOffset) THEN
				x.value := code.pc-orgOffset;
				x.type := ConstantInteger; (* TODO: should it be 'x.type := Offset'? *)
				RETURN TRUE;
			ELSIF GetIdentifier(pos,identifier) THEN
				label := labels.Find (identifier);
				IF label # NIL THEN
					x.value := label.offset;
					x.type := Offset;
					(*! deal with fixups ? / enter fixup ? *)
					RETURN TRUE;
				ELSIF GetConstant(errorPosition, identifier,x) THEN RETURN TRUE
				ELSIF ~critical & (pass # MaxPasses) THEN
					x.value := 0; x.type := ConstantInteger; RETURN TRUE
				ELSE Error(pos,"undefined symbol"); RETURN FALSE
				END;
			ELSIF ThisSymbol(Scanner.LeftParenthesis)  THEN
				RETURN Expression (x, critical) & ExpectSymbol(Scanner.RightParenthesis);
			END;
			RETURN FALSE
		END Factor;

		(* term = Factor { ( "*" | "/" | "%" ) Factor } *)
		PROCEDURE Term (VAR x: Result; critical: BOOLEAN): BOOLEAN;
		VAR y: Result; op : LONGINT;
		BEGIN
			IF Factor (x, critical) THEN
				WHILE (token.symbol = Scanner.Times) OR (token.symbol = Scanner.Div) OR (token.symbol = Scanner.Mod) DO
					op := token.symbol; NextToken;
					IF Factor (y, critical) THEN
						IF (x.type IN ConstantIntegerOrOffset) & (y.type IN ConstantIntegerOrOffset) THEN
							IF op = Scanner.Times THEN x.value := x.value * y.value
							ELSIF op = Scanner.Div THEN x.value := x.value DIV y.value
							ELSE x.value := x.value MOD y.value
							END;
						ELSIF (x.type = ConstantFloat) OR (y.type = ConstantFloat) THEN
							IF op = Scanner.Times THEN x.valueR := x.valueR * y.valueR
							ELSIF op = Scanner.Div THEN x.valueR := x.valueR / y.valueR
							ELSE RETURN FALSE
							END;
						ELSE RETURN FALSE
						END;
					ELSE
						RETURN FALSE;
					END;
				END;
				RETURN TRUE;
			ELSE
				RETURN FALSE;
			END;
		END Term;

		(* Expression = [ "-" | "+" | "~" ] Term { ( "+" | "-" ) Term } *)
		PROCEDURE Expression*(VAR x: Result; critical: BOOLEAN): BOOLEAN;
		VAR y: Result; op : LONGINT;
		BEGIN
			op := token.symbol;
			IF ThisSymbol(Scanner.Minus) THEN
				IF Term (x, critical) THEN
					IF x.type IN ConstantIntegerOrOffset THEN
						x.value := -x.value; x.valueR := x.value
					ELSIF x.type = ConstantFloat THEN
						x.valueR := -x.valueR
					ELSE
						RETURN FALSE
					END;
				ELSE
					RETURN FALSE;
				END;
			ELSIF ThisSymbol(Scanner.Plus) THEN
				IF ~Term (x, critical) THEN RETURN FALSE
				ELSE
					RETURN (x.type IN ConstantIntegerOrOffset) OR (x.type = ConstantFloat)
				END;
			ELSIF ThisSymbol(Scanner.Not) THEN
				IF Term (x, critical) THEN
					IF x.type IN ConstantIntegerOrOffset THEN
						x.value := -x.value-1; x.valueR := x.value
					ELSE
						RETURN FALSE
					END
				END;
			ELSIF ~Term (x, critical) THEN RETURN FALSE
			END;
			WHILE (token.symbol = Scanner.Plus) OR (token.symbol = Scanner.Minus) DO
				op := token.symbol; NextToken;
				IF Term (y, critical) THEN
					IF op = Scanner.Plus THEN
						IF (x.type IN ConstantIntegerOrOffset) & (y.type IN ConstantIntegerOrOffset) THEN
							x.value := x.value+y.value; x.valueR := x.value;
						ELSIF (x.type = ConstantFloat) & (y.type = ConstantFloat) THEN
							x.valueR := x.valueR + y.valueR;
						ELSE RETURN FALSE
						END;
					ELSE
						IF (x.type IN ConstantIntegerOrOffset) & (y.type IN ConstantIntegerOrOffset) THEN
							x.value := x.value-y.value; x.valueR := x.value;
						ELSIF (x.type = ConstantFloat) & (y.type = ConstantFloat) THEN
							x.valueR := x.valueR - y.valueR;
						ELSE RETURN FALSE
						END;
					END;
				ELSE
					RETURN FALSE;
				END;
			END;
			RETURN TRUE;
		END Expression;

		PROCEDURE Data(CONST ident: ARRAY OF CHAR): BOOLEAN;
		VAR size,i,nr: LONGINT; x: Result; pos: Position; result: Result; patterns: ObjectFile.FixupPatterns;
			PROCEDURE Number(ch: CHAR; VAR nr: LONGINT): BOOLEAN;
			BEGIN
				IF (ch >= "0") & (ch <="9") THEN
					nr := ORD(ch)-ORD("0");
					RETURN TRUE
				ELSE
					RETURN FALSE
				END;
			END Number;

		BEGIN
			size := -1;
			IF (ident = "DB") OR (ident = "db") THEN size := 8
			ELSIF (ident="DW") OR (ident = "dw") THEN size := 16
			ELSIF (ident="DD") OR (ident = "dd") THEN size := 32
			ELSIF (ident="DQ") OR (ident = "dq") THEN size := 64
			ELSIF (CAP(ident[0]) ="D") THEN
				size := 0;i := 1;
				WHILE Number(ident[i],nr) DO
					size := size*10+nr; INC(i);
				END;
				IF ident[i] # 0X THEN size := -1 END;
			END;
			IF size = -1 THEN RETURN FALSE
			ELSE
				IF Trace THEN D.String("Data"); D.Ln; END;
				REPEAT
					pos := errorPosition;
					IF token.symbol = Scanner.String THEN
						IF (pass = MaxPasses) & (code.comments # NIL) THEN
							code.comments.String(ident); section.comments.String(' "');
							code.comments.String(token.string^);
							code.comments.String('"');
							code.comments.Ln;
							code.comments.Update
						END;
						i := 0;
						WHILE token.string[i] # 0X DO
							PutBitsIfLastPass(ORD(token.string[i]),size);
							INC(i);
						END;
						NextToken;

					ELSIF (token.symbol = Scanner.Identifier) & GetNonConstant(errorPosition,token.identifierString,result) THEN
						IF (pass = MaxPasses) & (code.comments # NIL) THEN
							code.comments.String(ident);
							code.comments.String(" ");
							code.comments.String(token.identifierString);
							code.comments.Ln;
							code.comments.Update
						END;

						(* if this is the last pass then enter the fixup to the generated code section *)
						IF pass = MaxPasses THEN
							result.fixup.SetFixupOffset(code.pc);
							code.fixupList.AddFixup(result.fixup);
							(* set fixup width *)
							NEW(patterns, 1);
							patterns[0].offset := 0; patterns[0].bits := size;
							result.fixup.InitFixup(result.fixup.mode, result.fixup.offset, result.fixup.symbol, result.fixup.symbolOffset, result.fixup.displacement, 0, patterns);
						END;

						PutBitsIfLastPass(0,size);
						NextToken;

					ELSIF Expression(x,FALSE) THEN
						IF x.type # ConstantInteger THEN Error(pos,"forbidden non-constant value") END;
						IF (pass = MaxPasses) & (code.comments # NIL) THEN
							code.comments.String(ident);
							code.comments.String(" ");
							(* code.comments.Int(x.value,1); *)

							(* print number in hexadecimal form *)
							code.comments.String("0");
							code.comments.Hex(x.value, -size DIV 4);
							code.comments.String("H");

							code.comments.Ln;
							code.comments.Update
						END;

						PutBitsIfLastPass(x.value,size);

					ELSE Error(pos,"expected string or expression");
					END;
				UNTIL error OR ~ThisSymbol(Scanner.Comma);
			END;
			RETURN TRUE
		END Data;

		PROCEDURE Reserve(CONST ident: ARRAY OF CHAR): BOOLEAN;
		BEGIN RETURN FALSE
		END Reserve;

		(** if the assembler is at the last pass: put bits into the binary code section, otherwise only increment the PC **)
		PROCEDURE PutBitsIfLastPass(data: HUGEINT; size: BinaryCode.Bits);
		VAR
			oldPC: LONGINT;
		BEGIN
			IF pass = MaxPasses THEN
				code.PutBits(data, size)
			ELSE
				oldPC := code.pc;
				ASSERT(size MOD code.os.unit = 0);
				code.SetPC(oldPC + size DIV code.os.unit)
			END
		END PutBitsIfLastPass;

		PROCEDURE Instruction*(CONST mnemonic: ARRAY OF CHAR);
		VAR numberOperands: LONGINT;

			PROCEDURE ParseOperand(pos: Position; numberOperand: LONGINT);
			(* stub, must be overwritten by implementation *)
			VAR operand: OperandString;
				result: Result; first: BOOLEAN; str: ARRAY 256 OF CHAR;
			BEGIN
				first := TRUE;
				WHILE ~error & (token.symbol # Scanner.Ln) & (token.symbol # Scanner.Comma) DO
					IF (token.symbol = Scanner.Identifier) & GetNonConstant(errorPosition,token.identifierString,result) THEN
							D.String("(* non constant ");
							D.String(token.identifierString); D.String("="); DumpResult(D.Log,result);
							D.String("*)");
					ELSIF (token.symbol = Scanner.Identifier) & GetConstant(errorPosition,token.identifierString,result) THEN
							D.String("(* constant ");
							DumpResult(D.Log,result);
							D.String("*)");
					END;
					IF first THEN first := FALSE ELSE Strings.Append(operand," ") END;
					Scanner.TokenToString(token, scanner.case, str);
					Strings.Append(operand, str);
					NextToken;
				END;
				IF Trace THEN
					D.String("operand= ");
					D.String(operand); IF token.symbol = Scanner.Comma THEN D.String(" , ") END;
				END;
			END ParseOperand;
		BEGIN
			IF Trace THEN
				D.String("Instruction= "); D.String(mnemonic);  D.String(" ");
			END;
			numberOperands := 0;
			IF ~ThisSymbol(Scanner.Ln) THEN
				REPEAT
					ParseOperand(errorPosition,numberOperands);
					INC(numberOperands);
				UNTIL error OR ~ThisSymbol(Scanner.Comma);
				IF ~error & ExpectSymbol(Scanner.Ln) THEN END;
			END;
			IF Trace THEN D.Ln END
		END Instruction;

		PROCEDURE IgnoreNewLines;
		BEGIN
			WHILE ThisSymbol(Scanner.Ln) DO END;
		END IgnoreNewLines;

		PROCEDURE DoAssemble();
		VAR result: Result; pos: Position; line,orgCodePos: LONGINT; identifier: Scanner.IdentifierString; context: Scanner.Context;
		BEGIN
			IF Trace THEN
				D.Str("DoAssemble: ");
				IF section # NIL THEN Basic.WriteSegmentedName(D.Log,section.name); D.Ln END;
			END;

			NEW(labels);
			NEW(results);

			scanner.GetContext(context);
			NextToken;
			IgnoreNewLines;
			WHILE ~error & (token.symbol # Scanner.Period) & (token.symbol # Scanner.EndOfText) DO
				IF ThisSymbol(Scanner.Number) THEN
					line := token.integer;
					IF ThisSymbol(Scanner.Colon) THEN (* line number *)
					ELSE Error(token.position,"Identifier expected");
					END;
				END;
				IF ExpectIdentifier(pos,identifier) THEN
					IF ThisSymbol(Scanner.Colon) THEN (* label *)
						DefineLabel(pos,identifier)
					ELSIF ThisIdentifier("equ") OR ThisSymbol(Scanner.Equal) THEN
						IF Expression(result,FALSE) THEN DefineResult(pos,identifier,result) END;
					ELSE scanner.SkipToEndOfLine; NextToken;
					END;
				END;
				IgnoreNewLines;
			END;

			orgCodePos := code.pc;
			FOR pass := 1 TO MaxPasses DO
				labels.ResetDisplacements; (* this is important as the displacement is corrected by code emission in a cummulative way *)
				code.SetPC(orgCodePos);
				SetContext(context);
				IgnoreNewLines;
				WHILE ~error & (token.symbol # Scanner.EndOfText) & (token.symbol # Scanner.Period) DO
					IF ThisSymbol(Scanner.Number) THEN
						line := token.integer;
						IF ThisSymbol(Scanner.Colon) THEN (* line number *)
						ELSE Error(token.position,"Identifier expected");
						END;
					END;
					IF ExpectIdentifier(pos,identifier) THEN
						IF ThisSymbol(Scanner.Colon) THEN (* label *)
							SetLabel(pos,identifier);
						ELSIF ThisIdentifier("equ") OR ThisSymbol(Scanner.Equal) THEN (* constant definition *)
							IF Expression(result,FALSE) THEN SetResult(identifier,result) END;
						ELSE
							IF identifier = "section" THEN
								Section()
							ELSIF Data(identifier) THEN
							ELSIF Reserve(identifier) THEN
							ELSIF identifier = "fixed" THEN
								IF ExpectConstantInteger(result,TRUE) THEN
									code.SetAlignment(TRUE,LONGINT(result.value))
								END;
							ELSIF ~error THEN
								errorPosition := pos;
								Instruction(identifier);
								(*
								IF ~error & ExpectSymbol(Scanner.Ln) THEN END;
								*)
							END;
						END;
					END;
					IgnoreNewLines;
				END;
			END;
			IF Trace THEN
				D.Str("END Assemble"); D.Ln;
			END
		END DoAssemble;

		PROCEDURE InlineAssemble*(scanner: Scanner.AssemblerScanner; section: IntermediateCode.Section; scope: SyntaxTree.Scope; module: Sections.Module);
		BEGIN
			ASSERT(module # NIL); ASSERT(scanner # NIL); ASSERT(section # NIL);
			ASSERT(section.resolved # NIL);
			SELF.scope := scope;
			SELF.module := module;
			SELF.scanner := scanner;
			SELF.section := section;
			SELF.code := section.resolved;
			DoAssemble;
		END InlineAssemble;

		PROCEDURE Assemble*(scanner: Scanner.AssemblerScanner);
		BEGIN
			ASSERT(scanner # NIL);
			SELF.scanner := scanner;
			module := NIL; section := NIL; scope := NIL;
			scanner.SetContext(scanner.startContext);
			DoAssemble;
		END Assemble;

		PROCEDURE AllSections*;
		VAR pos: Position; sectionType, sectionName: Scanner.IdentifierString;
		BEGIN
			IF Trace THEN D.String("AllSections"); D.Ln END;
			SetContext(scanner.startContext);
			IgnoreNewLines;
			WHILE ThisSymbol(Scanner.Period) & ExpectIdentifier(pos,sectionType) & ExpectIdentifier(pos,sectionName) DO
				D.String("section "); D.String(sectionType); D.String(" "); D.String(sectionName); D.Ln;
				DoAssemble;
			END;
		END AllSections;

		PROCEDURE Text*(scanner: Scanner.AssemblerScanner);
		BEGIN
			ASSERT(scanner # NIL);
			SELF.scanner := scanner;
			module := NIL; section := NIL; scope := NIL;
			AllSections;
		END Text;

	END Assembler;

	PROCEDURE DumpResult*(w: Streams.Writer; result: Result);
	BEGIN
		CASE result.type OF
			ConstantInteger: w.String("i"); w.Int(result.sizeInBits,1);w.String(" ");w.Int(result.value,1);
			|ConstantFloat: w.String("f");w.Int(result.sizeInBits,1);w.String(" ");w.Float(result.value,20);
			|Offset: w.String("ofs "); w.Int(result.value,1);
			|Fixup: w.String("i"); w.Int(result.sizeInBits,1);w.String(" "); w.String("fixup ");
				result.fixup.Dump(w);
		END;
	END DumpResult;

	PROCEDURE Test*(context: Commands.Context);
	VAR scanner: Scanner.AssemblerScanner;  diagnostics: Diagnostics.StreamDiagnostics; assembler: Assembler;
	BEGIN
		NEW(diagnostics,context.out);
		scanner := Scanner.NewAssemblerScanner("command",context.arg,0,diagnostics);
		NEW(assembler,diagnostics);
		assembler.Text(scanner);
		(*
		assembler.Assemble(scanner);
		*)
	END Test;

	PROCEDURE TestScanner*(context: Commands.Context);
	VAR scanner: Scanner.AssemblerScanner;  diagnostics: Diagnostics.StreamDiagnostics; token: Scanner.Token;
	BEGIN
		NEW(diagnostics,context.out);
		scanner := Scanner.NewAssemblerScanner("command",context.arg,0,diagnostics);
		WHILE scanner.GetNextToken(token) & (token.symbol # Scanner.EndOfText)  DO
			Scanner.PrintToken(context.out, token); context.out.Ln;
		END;
	END TestScanner;

END FoxAssembler.

System.Free FoxAssembler ~

FoxAssembler.Test
;---------------- intermediate code -----------------
.module BitSets

.imports SYSTEM

.const BitSets.@moduleSelf offset=0
	0: data u32 0

.const BitSets.BitSet offset=0
	0: data u32 0

.code BitSets.BitSet.InitBitSet offset=0
	0: enter  0,  0
	1: mov u32 r1, u32 [fp+8]
	2: mov s32 [r1], s32 [fp+12]
	3: push s32 [fp+12]
	4: mov u32 r2, u32 [fp+8]
	5: add u32 r3, u32 [r2-4], u32 -88
	6: push u32 r2
	7: call u32 [r3],  8
	8: leave  0
	9: exit  8

.code BitSets.BitSet.Zero offset=0
	0: enter  0,  8
	1: mov s32 [fp-4], s32 0
	2: mov u32 r1, u32 [fp+8]
	3: mov u32 r2, u32 [r1+4]
	4: conv s32 r3, u32 [r2+12]
	5: sub s32 r3, s32 r3, s32 1
	6: mov s32 [fp-8], s32 r3
	7: brlt u32 BitSets.BitSet.Zero:21, s32 [fp-8], s32 [fp-4]
	8: br u32 BitSets.BitSet.Zero:9
	9: conv u32 r4, s32 [fp-4]
	10: mov u32 r5, u32 r4
	11: mov u32 r6, u32 [fp+8]
	12: mov u32 r7, u32 [r6+4]
	13: brlt u32 BitSets.BitSet.Zero:15, u32 r4, u32 [r7+12]
	14: trap  7
	15: mul u32 r5, u32 r5, u32 4
	16: add u32 r5, u32 r5, u32 r7+16
	17: mov u32 [r5], u32 0
	18: add s32 r8, s32 [fp-4], s32 1
	19: mov s32 [fp-4], s32 r8
	20: br u32 BitSets.BitSet.Zero:7
	21: leave  0
	22: exit  4

.code BitSets.BitSet.Resize offset=0
	0: enter  0,  12
	1: brlt u32 BitSets.BitSet.Resize:3, s32 [fp+12], s32 0
	2: br u32 BitSets.BitSet.Resize:4
	3: trap  8
	4: mov u32 r1, u32 [fp+8]
	5: mov s32 [r1], s32 [fp+12]
	6: sub s32 r2, s32 [fp+12], s32 1
	7: brlt u32 BitSets.BitSet.Resize:10, s32 r2, s32 0
	8: mov s32 r2, s32 r2
	9: br u32 BitSets.BitSet.Resize:11
	10: mov s32 r2, s32 0, s32 r2
	11: shr s32 r2, s32 r2, s32 5
	12: add s32 r2, s32 r2, s32 1
	13: mov s32 [fp+12], s32 r2
	14: mov u32 r3, u32 [fp+8]
	15: breq u32 BitSets.BitSet.Resize:35, u32 [r3+4], u32 0
	16: br u32 BitSets.BitSet.Resize:17
	17: mov u32 r4, u32 [fp+8]
	18: mov u32 r5, u32 [r4+4]
	19: conv s32 r6, u32 [r5+12]
	20: brlt u32 BitSets.BitSet.Resize:25, s32 r6, s32 [fp+12]
	21: br u32 BitSets.BitSet.Resize:22
	22: leave  0
	23: exit  8
	24: br u32 BitSets.BitSet.Resize:25
	25: mov u32 r7, u32 [fp+8]
	26: mov u32 r8, u32 [r7+4]
	27: conv s32 r9, u32 [r8+12]
	28: shl s32 r9, s32 r9, s32 1
	29: brlt u32 BitSets.BitSet.Resize:32, s32 [fp+12], s32 r9
	30: mov s32 r9, s32 [fp+12]
	31: br u32 BitSets.BitSet.Resize:33
	32: mov s32 r9, s32 r9, s32 r9
	33: mov s32 [fp+12], s32 r9
	34: br u32 BitSets.BitSet.Resize:35
	35: brge u32 BitSets.BitSet.Resize:37, s32 [fp+12], s32 0
	36: trap  9
	37: push s32 [fp+12]
	38: mov s32 r10, s32 [fp+12]
	39: conv u32 r10, s32 r10
	40: mul u32 r10, u32 r10, u32 4
	41: add u32 r10, u32 r10, u32 16
	42: push u32 fp-4
	43: push u32 fp-4
	44: push u32 r10
	45: push u8 0
	46: call u32 $SystemCall2:0,  0
	47: pop u32 r11
	48: mov u32 r12, u32 [r11]
	49: breq u32 BitSets.BitSet.Resize:53, u32 r12, u32 0
	50: pop u32 r13
	51: mov u32 [r12+12], u32 r13
	52: br u32 BitSets.BitSet.Resize:54
	53: add u32 sp, u32 sp, u32 4
	54: mov u32 r14, u32 [fp+8]
	55: breq u32 BitSets.BitSet.Resize:85, u32 [r14+4], u32 0
	56: br u32 BitSets.BitSet.Resize:57
	57: mov s32 [fp-8], s32 0
	58: mov u32 r15, u32 [fp+8]
	59: mov u32 r16, u32 [r15+4]
	60: conv s32 r17, u32 [r16+12]
	61: sub s32 r17, s32 r17, s32 1
	62: mov s32 [fp-12], s32 r17
	63: brlt u32 BitSets.BitSet.Resize:84, s32 [fp-12], s32 [fp-8]
	64: br u32 BitSets.BitSet.Resize:65
	65: conv u32 r18, s32 [fp-8]
	66: mov u32 r19, u32 r18
	67: mov u32 r20, u32 [fp+8]
	68: mov u32 r21, u32 [r20+4]
	69: brlt u32 BitSets.BitSet.Resize:71, u32 r18, u32 [r21+12]
	70: trap  7
	71: mul u32 r19, u32 r19, u32 4
	72: add u32 r19, u32 r19, u32 r21+16
	73: conv u32 r22, s32 [fp-8]
	74: mov u32 r23, u32 r22
	75: mov u32 r24, u32 [fp-4]
	76: brlt u32 BitSets.BitSet.Resize:78, u32 r22, u32 [r24+12]
	77: trap  7
	78: mul u32 r23, u32 r23, u32 4
	79: add u32 r23, u32 r23, u32 r24+16
	80: mov u32 [r23], u32 [r19]
	81: add s32 r25, s32 [fp-8], s32 1
	82: mov s32 [fp-8], s32 r25
	83: br u32 BitSets.BitSet.Resize:63
	84: br u32 BitSets.BitSet.Resize:85
	85: mov u32 r26, u32 [fp+8]
	86: mov u32 [r26+4], u32 [fp-4]
	87: leave  0
	88: exit  8

.code BitSets.BitSet.GetSize offset=0
	0: enter  0,  0
	1: mov u32 r1, u32 [fp+8]
	2: return s32 [r1]
	3: leave  0
	4: exit  4
	5: trap  3