Giuga numbers: Difference between revisions

=={{header|PL/M}}==

{{works with|8080 PL/M Compiler}} ... under CP/M (or an emulator)

Only finds 3 Giuga numbers as the fourth is larger than 65535, the largest integer supported by the 8080 PL/M compiler.

<syntaxhighlight lang="plm">

100H: /* FIND SOME GIUGA NUMBERS, COMPOSITES N SUCH THAT ALL THEIR DISTINCT */

/* PRIME FACTORS F EXACTLY DIVIDE ( N / F ) - 1 */

/* CP/M BDOS SYSTEM CALL AND I/O ROUTINES */

BDOS: PROCEDURE( FN, ARG ); DECLARE FN BYTE, ARG ADDRESS; GOTO 5; END;

PR$CHAR: PROCEDURE( C ); DECLARE C BYTE; CALL BDOS( 2, C ); END;

PR$STRING: PROCEDURE( S ); DECLARE S ADDRESS; CALL BDOS( 9, S ); END;

PR$NL: PROCEDURE; CALL PR$CHAR( 0DH ); CALL PR$CHAR( 0AH ); END;

PR$NUMBER: PROCEDURE( N ); /* PRINTS A NUMBER IN THE MINIMUN FIELD WIDTH */

DECLARE N ADDRESS;

DECLARE V ADDRESS, N$STR ( 6 )BYTE, W BYTE;

V = N;

W = LAST( N$STR );

N$STR( W ) = '$';

N$STR( W := W - 1 ) = '0' + ( V MOD 10 );

DO WHILE( ( V := V / 10 ) > 0 );

N$STR( W := W - 1 ) = '0' + ( V MOD 10 );

END;

CALL PR$STRING( .N$STR( W ) );

END PR$NUMBER;

/* TASK */

/* FIND THE FIRST THREE GIUGA NUMBERS (THE FOURTH IS > 65535) */

/* EACH PRIME FACTOR CAN ONLY APPEAR ONCE, E.G.,: FOR 2: */

/* (( N / 2 ) - 1) MOD 2 = 0 => N / 2 IS ODD => N NOT DIVISIBLE BY 4 */

/* SIMILARLY FOR OTHER PRIMES */

DECLARE ( N, V, FCOUNT, F ) ADDRESS;

DECLARE IS$GIUGA BYTE;

N = 2;

DO WHILE N < 65000; /* ASSUME THE NUMEBRS ARE ALL EVEN */

V = N / 2;

IS$GIUGA = 1;

FCOUNT = 1;

F = 1;

DO WHILE ( F := F + 2 ) <= V AND IS$GIUGA;

IF V MOD F = 0 THEN DO;

/* HAVE A PRIME FACTOR */

FCOUNT = FCOUNT + 1;

IS$GIUGA = ( ( N / F ) - 1 ) MOD F = 0;

V = V / F;

END;

END;

IF IS$GIUGA THEN DO;

IF FCOUNT > 1 THEN DO;

/* N IS NOT PRIME, SO IS GIUGA */

CALL PR$CHAR( ' ' );CALL PR$NUMBER( N );

END;

END;

N = N + 4;

END;

EOF

</syntaxhighlight>

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30 858 1722

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