lang/m2/test/Wirth/PowersOf2.mod

   1 MODULE PowersOf2;
   2   FROM InOut IMPORT Write, WriteLn, WriteString, WriteCard;
   3
   4   CONST
   5         M = 11;         (* M ~ N*log(2) *)
   6         N = 32;
   7   VAR
   8         i,j,k,exp: CARDINAL;
   9         c,r,t:  CARDINAL;
  10         d: ARRAY [0..M] OF CARDINAL;
  11         f: ARRAY[0..N] OF CARDINAL;
  12   BEGIN
  13         d[0] := 1;
  14         k := 1;
  15         FOR exp := 1 TO N DO
  16                 (* compute d = 2 ^ exp by d = 2*d *)
  17                 c := 0;         (* carry *)
  18                 FOR i := 0 TO k-1 DO
  19                         t := 2 * d[i] + c;
  20                         IF t >= 10 THEN
  21                                 d[i] := t - 10;
  22                                 c := 1;
  23                         ELSE
  24                                 d[i] := t;
  25                                 c := 0;
  26                         END
  27                 END;
  28                 IF c > 0 THEN
  29                         d[k] := 1;
  30                         k := k + 1
  31                 END;
  32                 (* output d[k-1] .. d[0] *)
  33                 i := M;
  34                 REPEAT
  35                         i := i - 1;
  36                         Write(" ")
  37                 UNTIL i = k;
  38                 REPEAT
  39                         i := i - 1;
  40                         Write(CHR(d[i]+ORD("0")))
  41                 UNTIL i = 0;
  42                 WriteCard(exp, 4);
  43                 (* compute and output f = 2^(-exp) by f := f DIV 2 *)
  44                 WriteString(" 0.");
  45                 r := 0;         (* remainder *)
  46                 FOR j := 1 TO exp-1 DO
  47                         r := 10 * r + f[j];
  48                         f[j] := r DIV 2;
  49                         r := r MOD 2;
  50                         Write(CHR(f[j]+ORD("0")))
  51                 END;
  52                 f[exp] := 5;
  53                 Write("5");
  54                 WriteLn
  55         END
  56   END PowersOf2.
  57