ftest6a.pll

一个嵌入式系统的C代码

PROGRAM FTEST6A (OUTPUT);

{--------------------------------------------------------------------}
{ Program to compute Prime Numbers based on a program taken from     }
{ "Programming In MODULA-2" - I knew this thing would come in handy  }
{ some day!  This overly complex algorithm is based on the idea of   }
{ inspecting the divisibility of successive integers.  The tested    }
{ integers are obtained by incrementing alternatly by 2 and 4 which  }
{ avoids multiples of 2 and 3 (which can't be prime).  Divisibility  }
{ only needs be tested for prime divisors, which are obtained by     }
{ storing previously computed resluts (Wirth, N., 1982).             }
{                                                                    }
{ 17-SEP-94 Modified to write to a text file (arcy)                  }
{--------------------------------------------------------------------}


CONST
  N = 500;
  M = 23;      { M ~= sqrt(N) }
  L = 04;      { Primes per lime }

VAR
  i, k, x, ncnt : INTEGER;
  inc, lim, square, opf : INTEGER;
  prime : INTEGER;
  P, V  : ARRAY [M] OF INTEGER;

BEGIN 
  ASSIGN(opf@, 'PRIMES.TXT');
  REWRITE(opf@);
  Writeln('File "PRIMES.TXT" created.');
  ncnt := 0;
  x := 1;
  inc := 4;
  lim := 1;
  square := 9;
  FOR i := 3 TO N DO BEGIN
    REPEAT
      x := X + inc;
      inc := 6 - inc;
      IF square <= x THEN BEGIN
	lim := lim + 1;
	V[lim] := square;
	square := P[lim+1] * P[lim+1]
      END;
      k := 2;
      prime := 1;
      WHILE (prime = 1) AND (k < lim) DO BEGIN
	k := K + 1;
	IF V[k] < x THEN
	  V[k] := V[k] + 2 * P[k];
	IF (x <> V[k]) THEN
	  prime := 1
	ELSE
	  prime := 0
      END
    UNTIL prime = 1;
    IF i <= M THEN
      P[i] := x;
    Writeln(opf@, x#);
    ncnt := ncnt + 1
  END;
  CLOSE(opf@);
  Writeln(ncnt#, 'records written.')
END.