Data commit

Task/Machine-code/PL-M/machine-code.plm

@@ -0,0 +1,68 @@
+100H:
+
+/* 8080 MACHINE CODE TO ADD TWO BYTES:
+   79       MOV A,C     ; LOAD FIRST ARG INTO ACCUMULATOR
+   83       ADD E       ; ADD SECOND ARG TO ACCUMULATOR
+   C9       RET         ; RETURN */
+
+DECLARE ADD$8080 DATA (79H, 83H, 0C9H);
+
+/* THE 8080 PL/M CALLING CONVENTION IS THAT THE
+   NEXT-TO-LAST ARG IS PUT IN (B)C, THE LAST ARG IN (D)E.
+   (THE REST ARE IN MEMORY BUT WE DO NOT NEED ANY MORE.)
+   THE RETURN ARGUMENT SHOULD BE IN THE ACCUMULATOR.
+   WE CAN DEFINE A WRAPPER PROCEDURE TO DECLARE THE
+   TYPES OF THE ARGUMENTS. */
+
+EXEC$ADD: PROCEDURE (A,B) BYTE;
+    DECLARE (A,B) BYTE;
+    /* WE CAN 'GO TO' CONSTANTS OR VARIABLES, BUT NOT TO
+       EXPRESSIONS. SO WE HAVE TO FETCH THE ADDRESS FIRST. */
+    DECLARE LOC ADDRESS;
+    LOC = .ADD$8080;
+    GO TO LOC;
+END EXEC$ADD;
+
+/* IN FACT, PL/M DOES NOT COME WITH ANY STANDARD LIBARIES.
+   IT IS FROM BEFORE THE TIME THAT YOU COULD ASSUME THERE
+   WOULD EVEN BE AN OPERATING SYSTEM, THOUGH CP/M
+   (THE PREDECESSOR TO DOS) WOULD QUICKLY BECOME STANDARD.
+
+   WE NEED TO USE THIS EXACT TRICK TO GET CP/M TO PRINT THE
+   RESULT TO THE OUTPUT. LUCKILY (AND NOT COINCIDENTALLY),
+   THE CP/M SYSCALL ENTRY POINT IS COMPATIBLE WITH THE
+   PL/M CALLING CONVENTION. */
+
+BDOS: PROCEDURE (FUNC, ARG);
+    DECLARE FUNC BYTE;
+    DECLARE ARG ADDRESS;
+    /* 5 IS THE CP/M BDOS ENTRY POINT */
+    GO TO 5;
+END BDOS;
+
+/* WE ALSO NEED OUR OWN NUMBER OUTPUT ROUTINE. WE CAN WRITE
+   IT IN PL/M, THEN USE THE ABOVE ROUTINE TO TELL CP/M
+   TO PRINT THE RESULT. */
+
+PRINT$NUMBER: PROCEDURE(N);
+    DECLARE S (4) BYTE INITIAL ('...$');
+    DECLARE P ADDRESS;
+    DECLARE (N, C BASED P) BYTE;
+
+    /* EXTRACT EACH DIGIT AND WRITE THEM BACKWARDS TO A STRING */
+    P = .S(3);
+DIGIT:
+    P = P-1;
+    C = (N MOD 10) + '0';
+    N = N/10;
+    IF N > 0 THEN GO TO DIGIT;
+
+    /* TELL CP/M TO PRINT THE RESULTING STRING */
+    CALL BDOS(9, P);
+END PRINT$NUMBER;
+
+/* USING OUR OWN MACHINE CODE WORKS IN THE SAME WAY */
+CALL PRINT$NUMBER( EXEC$ADD( 7, 12) ); /* THIS PRINTS 19 */
+
+CALL BDOS(0,0); /* EXIT */
+EOF