Data commit

Task/Subleq/XPL0/subleq.xpl0

@@ -0,0 +1,52 @@
+\Subleq program interpreter
+
+    \Executes the program specified in scode, stops when the instruction
+    \ pointer becomes negative.
+    procedure RunSubleq ( SCode, CodeLength);
+    integer   SCode, CodeLength;
+    define  MaxMemory = 3 * 1024;
+    integer Memory ( MaxMemory );
+    integer IP, A, B, C, I;
+    begin
+        begin
+            for I := 0 to MaxMemory - 1 do Memory( I ) := 0;
+            \Load the program into Memory
+            for I := 0 to CodeLength do Memory( I ) := SCode( I );
+            \Start at instruction 0
+            IP := 0;
+            \Execute the instructions to 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
+                    Memory( B ) := ChIn(1)
+                    end
+                else if B = -1 then begin
+                    \Output character from A
+                    ChOut(0, Memory ( A ) )
+                    end
+                else begin
+                    \Subtract and branch if <= 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
+    integer Code;
+    begin
+        Code := [ 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 ];
+        RunSubleq( Code, 31 )
+    end