Implement local labels (1b, 2f) like in GNU assembler.

src/rars/ProgramStatement.java

@@ -231,7 +231,7 @@ public void buildBasicStatementFromBasicInstruction(ErrorList errors) {
                 this.operands[this.numOperands++] = rounding_mode;
             } else if (tokenType == TokenTypes.IDENTIFIER) {
 
-                int address = this.sourceProgram.getLocalSymbolTable().getAddressLocalOrGlobal(tokenValue);
+                int address = this.sourceProgram.getLocalSymbolTable().getAddressLocalOrGlobal(tokenValue, token.getSourceLine());
                 if (address == SymbolTable.NOT_FOUND) { // symbol used without being defined
                     errors.add(new ErrorMessage(this.sourceProgram, token.getSourceLine(), token.getStartPos(),
                             "Symbol \"" + tokenValue + "\" not found in symbol table."));

src/rars/assembler/Assembler.java

@@ -575,7 +575,8 @@ private boolean tokenListBeginsWithLabel(TokenList tokens) {
         // 2-July-2010. DPS. Remove prohibition of operator names as labels
         if (tokens.size() < 2)
             return false;
-        return (tokens.get(0).getType() == TokenTypes.IDENTIFIER || tokens.get(0).getType() == TokenTypes.OPERATOR)
+        TokenTypes type0 = tokens.get(0).getType();
+        return (type0 == TokenTypes.IDENTIFIER || type0 == TokenTypes.OPERATOR || type0 == TokenTypes.INTEGER_5)
                 && tokens.get(1).getType() == TokenTypes.COLON;
     }
 
@@ -1002,7 +1003,7 @@ private void storeInteger(Token token, Directives directive, ErrorList errors) {
         else if (token.getType() == TokenTypes.IDENTIFIER) {
             if (this.inDataSegment) {
                 int value = fileCurrentlyBeingAssembled.getLocalSymbolTable()
-                        .getAddressLocalOrGlobal(token.getValue());
+                        .getAddressLocalOrGlobal(token.getValue(), token.getSourceLine());
                 if (value == SymbolTable.NOT_FOUND) {
                     // Record value 0 for now, then set up backpatch entry
                     int dataAddress = writeToDataSegment(0, lengthInBytes, token, errors);
@@ -1327,7 +1328,7 @@ private void resolve(SymbolTable localSymtab) {
             DataSegmentForwardReference entry;
             for (int i = 0; i < forwardReferenceList.size(); i++) {
                 entry = forwardReferenceList.get(i);
-                labelAddress = localSymtab.getAddressLocalOrGlobal(entry.token.getValue());
+                labelAddress = localSymtab.getAddressLocalOrGlobal(entry.token.getValue(), entry.token.getSourceLine());
                 if (labelAddress != SymbolTable.NOT_FOUND) {
                     // patch address has to be valid b/c we already stored there...
                     try {

src/rars/assembler/Symbol.java

@@ -11,6 +11,7 @@ public class Symbol {
     private String name;
     private int address;
     private boolean data; // boolean true if data symbol false if text symbol.
+    private int sourceLine;
 
     /**
      * Basic constructor, creates a symbol object.
@@ -20,10 +21,11 @@ public class Symbol {
      * @param data    true if it represents data, false if code.
      **/
 
-    public Symbol(String name, int address, boolean data) {
+    public Symbol(String name, int address, boolean data, int sourceLine) {
         this.name = name;
         this.address = address;
         this.data = data;
+        this.sourceLine = sourceLine;
     }
 
     /**
@@ -57,6 +59,11 @@ public boolean getType() {
     }
 
 
+    public int getSourceLine() {
+        return this.sourceLine;
+    }
+
+
     /**
      * Sets (replaces) the address of the the Symbol.
      *

src/rars/assembler/SymbolTable.java

@@ -44,10 +44,10 @@ public SymbolTable(String filename) {
 
     public void addSymbol(Token token, int address, boolean b, ErrorList errors) {
         String label = token.getValue();
-        if (getSymbol(label) != null) {
+        if (getSymbol(label) != null && !Character.isDigit(label.charAt(0))) {
             errors.add(new ErrorMessage(token.getSourceProgram(), token.getSourceLine(), token.getStartPos(), "label \"" + label + "\" already defined"));
         } else {
-            table.add(new Symbol(label, address, b));
+            table.add(new Symbol(label, address, b, token.getSourceLine()));
             if (Globals.debug)
                 System.out.println("The symbol " + label + " with address " + address + " has been added to the " + this.filename + " symbol table.");
         }
@@ -90,6 +90,23 @@ public int getAddress(String s) {
         return NOT_FOUND;
     }
 
+    public int getLocalAddress(String s, int sourceLine) {
+        if (s.length() == 2 && Character.isDigit(s.charAt(0))) {
+            String label = s.substring(0, 1);
+            var matching = table.stream()
+                .filter(sym -> sym.getName().equals(label))
+                .sorted((a, b) -> Integer.compare(a.getSourceLine(), b.getSourceLine()));
+            if (s.charAt(1) == 'f') {
+                return matching.filter(sym -> sym.getSourceLine() > sourceLine)
+                    .findFirst().map(Symbol::getAddress).orElse(NOT_FOUND);
+            } else {
+                return matching.filter(sym -> sym.getSourceLine() <= sourceLine)
+                    .reduce((first, last) -> last).map(Symbol::getAddress).orElse(NOT_FOUND);
+            }
+        }
+        return getAddress(s);
+    }
+
     /**
      * Method to return the address associated with the given label.  Look first
      * in this (local) symbol table then in symbol table of labels declared
@@ -98,8 +115,8 @@ public int getAddress(String s) {
      * @param s The label.
      * @return The memory address of the label given, or NOT_FOUND if not found in symbol table.
      **/
-    public int getAddressLocalOrGlobal(String s) {
-        int address = this.getAddress(s);
+    public int getAddressLocalOrGlobal(String s, int sourceLine) {
+        int address = this.getLocalAddress(s, sourceLine);
         return (address == NOT_FOUND) ? Globals.symbolTable.getAddress(s) : address;
     }
 

src/rars/assembler/TokenTypes.java

@@ -151,6 +151,11 @@ public static TokenTypes matchTokenType(String value) {
             // NO ACTION -- exception suppressed
         }
 
+        // See if it is a local label reference like 1b or 2f
+        if (value.length() == 2 && Character.isDigit(value.charAt(0)) &&
+                (value.charAt(1) == 'f' || value.charAt(1) == 'b'))
+            return TokenTypes.IDENTIFIER;
+
         // See if it is a real (fixed or floating point) number.  Note that parseDouble()
         // accepts integer values but if it were an integer literal we wouldn't get this far.
         if (value.equals("Inf") || value.equals("NaN")) return TokenTypes.REAL_NUMBER;
@@ -179,7 +184,7 @@ public static TokenTypes matchTokenType(String value) {
             return TokenTypes.OPERATOR;
 
         // Test for identifier goes last because I have defined tokens for various
-        // MIPS constructs (such as operators and directives) that also could fit
+        // constructs (such as operators and directives) that also could fit
         // the lexical specifications of an identifier, and those need to be
         // recognized first.
         if (isValidIdentifier(value))
@@ -190,7 +195,7 @@ public static TokenTypes matchTokenType(String value) {
     }
 
     /**
-     * Lets you know if given tokentype is for integers (INTGER_5, INTEGER_16, INTEGER_32).
+     * Lets you know if given tokentype is for integers (INTEGER_5, INTEGER_16, INTEGER_32).
      *
      * @param type the TokenType of interest
      * @return true if type is an integer type, false otherwise.

test/local-labels.s

@@ -0,0 +1,21 @@
+#exit:42
+.globl main
+.text
+main:
+	# Tests simple looping behaviour
+	li t0, 60
+	li t1, 0
+1:
+	addi t1, t1, 5
+	addi t0, t0, -1
+	bne t1, t0, 1b
+	bne t1, zero, 1f
+2:
+	li a0, 0
+	li a7, 93
+	ecall
+
+1:
+	li a0, 42
+	li a7, 93
+	ecall