{
Depending on the application, BCD may solve your problem. But if you
really need a _large_ binary integer you are going to have to use
multiple precision arithmetic. This is relatively easy to do in assembler
and just a little more difficult in a high-level language.
You need to define your _integer_ as an array of 256 bytes, 128 words,
or 64 unsigned long integers. So we're stuck with words. So our bigint
is an array[0..127] of word; We'll do it little-endian 0=least
significant word, 127 = most significant word. Using words with a longint
intermediate value actually makes our task a little easier.
}
CONST MaxBIG = 127;
TYPE tBigInt = Array[0..MaxBIG] of Word;
PROCEDURE BigAdd(VAR Op1, Op2: tBigInt);
{ --------------------------------------------- }
{ Do multiprecision add: Op1 := Op1 + Op2 }
{ --------------------------------------------- }
VAR i: Integer;
Temp: Longint;
Begin
Temp := 0; { Clear carry }
For i := 0 to MaxBIG Do Begin
Temp := Longint(Op1[i]) + Op2[i] + Temp;
Op1[i] := Word(Temp);
Temp := Temp shr 16; { Carry = High word }
End;
END;
PROCEDURE BigSub(VAR Op1, Op2: tBigInt);
{ --------------------------------------------- }
{ Do multiprecision Substract: Op1 := Op1 - Op2 }
{ --------------------------------------------- }
VAR i: Integer;
Temp: Longint;
Begin
Temp := 0; { Clear carry }
For i := 0 to MaxBIG Do Begin
Temp := Longint(Op1[i]) - Op2[i] - Temp;
Op1[i] := Word(Temp);
Temp := Temp shr 16; { Carry = High word }
End;
END;
I've done the easy part. It's your turn to put together
the multiprecision multiply and divide. If Op2 can be
an integer I'll toss together an op1*Op2 and Op1 div Op2.
But for a full version I'd have to crack the books :-)