C/C ++ algorithm example (5)-high-precision computing

Definition of high precision data:
Type
HP = array [1 .. maxlen] of integer;

1. High-Precision Addition

Procedure plus (A, B: HP; var C: HP );
VaR I, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
If a [0]> B [0] Then Len: = A [0] else Len: = B [0];
For I: = 1 to Len do begin
INC (C [I], a [I] + B [I]);
If C [I]> 10 then begin Dec (C [I], 10); Inc (C [I + 1]); end; {carry}
End;
If C [Len + 1]> 0 then Inc (LEN );
C [0]: = Len;
End; {plus}

2. High-Precision Subtraction
Procedure substract (A, B: HP; var C: HP );

VaR I, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
If a [0]> B [0] Then Len: = A [0] else Len: = B [0];
For I: = 1 to Len do begin
INC (C [I], a [I]-B [I]);
If C [I] <0 then begin Inc (C [I], 10); Dec (C [I + 1]); end;
While (LEN> 1) and (C [Len] = 0) Do Dec (LEN );
C [0]: = Len;
End;

3. High Precision multiplied by low precision

Procedure multiply (A: HP; B: longint; var C: HP );
VaR I, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
Len: = A [0];
For I: = 1 to Len do begin
INC (C [I], a [I] * B );
INC (C [I + 1], (a [I] * B) Div 10 );
C [I]: = C [I] mod 10;
End;
INC (LEN );
While (C [Len]> = 10) Do begin {process the carry of the highest bit}
C [Len + 1]: = C [Len] Div 10;
C [Len]: = C [Len] mod 10;
INC (LEN );
End;
While (LEN> 1) and (C [Len] = 0) Do Dec (LEN); {adjust Len if carry is not needed}
C [0]: = Len;
End; {multiply}

4. High Precision multiplied by High Precision

Procedure high_multiply (A, B: HP; var C: HP}
VaR I, j, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
For I: = 1 to a [0] Do
For J: = 1 to B [0] Do begin
INC (C [I + J-1], a [I] * B [J]);
INC (C [I + J], C [I + J-1] Div 10 );
C [I + J-1]: = C [I + J-1] mod 10;
End;
Len: = A [0] + B [0] + 1;
While (LEN> 1) and (C [Len] = 0) Do Dec (LEN );
C [0]: = Len;
End;

5. High Precision divided by low precision

Procedure devide (A: HP; B: longint; var C: HP; var D: longint );
{C: = a div B; D: = a mod B}
VaR I, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
Len: = A [0]; D: = 0;
For I: = Len downto 1 do begin
D: = D * 10 + A [I];
C [I]: = D Div B;
D: = D mod B;
End;
While (LEN> 1) and (C [Len] = 0) Then Dec (LEN );
C [0]: = Len;
End;

6. High Precision divided by High Precision

Procedure high_devide (A, B: HP; var C, D: HP );
VaR
I, Len: integer;
Begin
Fillchar (C, sizeof (C), 0 );
Fillchar (D, sizeof (D), 0 );
Len: = A [0]; d [0]: = 1;
For I: = Len downto 1 do begin
Multiply (D, 10, d );
D [1]: = A [I];
While (compare (D, B)> = 0) do {that is, D> = B}
Begin
Subtract (D, B, d );
INC (C [I]);
End;
End;
While (LEN> 1) and (C. s [Len] = 0) Do Dec (LEN );
C. Len: = Len;
End;