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