Data commit

Task/Subleq/ALGOL-W/subleq.alg

@@ -0,0 +1,66 @@
+% Subleq program interpreter                                                 %
+begin
+
+    % executes the program specified in scode, stops when the instruction    %
+    % pointer becomes negative                                               %
+    procedure runSubleq ( integer array scode( * )
+                        ; integer value codeLength
+                        ) ;
+    begin
+        integer maxMemory;
+        maxMemory := 3 * 1024;
+        begin
+            integer array memory ( 0 :: maxMemory - 1 );
+            integer       ip, a, b, c;
+            for i := 0 until maxMemory - 1 do memory( i ) := 0;
+            % load the program into memory                                   %
+            for i := 0 until codeLength do memory( i ) := scode( i );
+
+            % start at instruction 0                                         %
+            ip := 0;
+            % execute the instructions until ip is < 0                       %
+            while ip >= 0 do begin
+                % get three words at ip and advance ip past them             %
+                a  := memory( ip     );
+                b  := memory( ip + 1 );
+                c  := memory( ip + 2 );
+                ip := ip + 3;
+                % execute according to a, b and c                            %
+                if       a = -1 then begin
+                    % input a character to b                                 %
+                    string(1) input;
+                    read( input );
+                    memory( b ) := decode( input )
+                    end
+                else if b = -1 then begin
+                    % output character from a                                %
+                    writeon( code( memory( a ) ) )
+                    end
+                else begin
+                    % subtract and branch if le 0                            %
+                    memory( b ) := memory( b ) - memory( a );
+                    if memory( b ) <= 0 then ip := c
+                end
+            end % while-do %
+        end
+    end % runSubleq % ;
+
+    % test the interpreter with the hello-world program specified in the task %
+    begin
+        integer array code ( 0 :: 31 );
+        integer       codePos;
+        codePos := 0;
+        for i :=  15,  17,  -1,  17,  -1,  -1
+               ,  16,   1,  -1,  16,   3,  -1
+               ,  15,  15,   0,   0,  -1,  72
+               , 101, 108, 108, 111,  44,  32
+               , 119, 111, 114, 108, 100,  33
+               ,  10,   0
+        do begin
+            code( codePos ) := i;
+            codePos := codePos + 1;
+        end;
+        runSubleq( code, 31 )
+    end
+
+end.