128 bit operation with delphi - delphi

Question

I need to convert a hexadecimal value to a decimal integer. Is there some unit that can do this?
On the web I have found something about it but it is not helping me much. I understood that using inline asm it is possible to represent it as a packed array of four 32 bit Integer. I have found as convert a int32 or int64 to int128 and viceversa, but not found nothing for take for example two int64 and to do a int128 and too i have found issue searching in asm inline something that emule div operator, mul operator and sum operator.
So I ask if someone can help me to solve this problem. My objective is to take a string in hexadecimal and convert it in decimal and after that calculate the equivalent value in base 35 (0..9, A..Z).
Thanks very much.

Answer 1

If you convert the hexadecimal string into an array of bytes (see SysUtils for that) you can use the follewing code to convert it into base 35:
function EncodeBaseX( const Values: array of Byte; var Dest: array of Byte; Radix: Integer ): Boolean;
var
i,j,Carry: Integer;
begin
// We're unsuccesful up to now
Result := False;
// Check if we have an output buffer and clear it
if Length( Dest ) = 0 then Exit;
System.FillChar( Dest[ 0 ], Length( Dest ), 0 );
// fill in the details
for i := 0 to High( Values ) do begin
Carry := Values[ i ];
for j := 0 to High( Dest ) do begin
Inc( Carry, Radix * Dest[ j ] );
Dest[ j ] := Carry and $ff;
Carry := Carry shr 8;
end;
if Carry <> 0 then Exit; // overflow
end;
// We're succesful
Result := True;
end;
{Bytes: array of byte (0..255); Dest: array of Byte(0..Radix-1)}
function DecodeBaseX( const Bytes: array of Byte; var Dest: array of Byte; Radix: Integer ): Boolean;
var
i,j,Carry: Integer;
B: array of Byte;
begin
// We're unsuccesful up to now
Result := False;
// Copy data
if Length( Bytes ) = 0 then Exit;
SetLength( B, Length( Bytes ) );
System.Move( Bytes[ 0 ], B[ 0 ], Length( B ) );
// fill in the details
for i := High( Dest ) downto 0 do begin
Carry := 0;
for j := High( Bytes ) downto 0 do begin
Carry := Carry shl 8 + B[ j ];
B[ j ] := Carry div Radix; Carry := Carry mod Radix;
end;
Dest[ i ] := Carry;
end;
// Check if we collected all the bits
Carry := 0;
for i := 0 to High( B ) do Carry := Carry or B[ i ];
// We're succesful if no bits stayed pending.
Result := ( Carry = 0 );
end;
Then transform the base 35 bytes into characters:
function EncodeKeyToString( const Num128Bits: array of Byte ): Ansistring;
var
Src: array [0..15] of Byte; // your 128 bits
Dest: array [0..24] of Byte;
i: Integer;
const
EncodeTable: AnsiString = '0123456789ABCDEFGHIJKLMNPQRSTUVWXYZ';
// O is not present to make base 35. If you want a different code, be my guest.
begin
// Convert to an array of 25 values between 0-35
System.Move( Num128Bits[ 0 ], Src[ 0 ], Length( Src ) ); // Copy data in our private placeholder
DecodeBaseX( Src, Dest, 35 );
// Convert to a representable string
SetLength( Result, Length( Dest ) );
for i := 0 to High( Dest ) do begin
Assert( Dest[ i ] < Length( EncodeTable ) );
Result[ i + 1 ] := EncodeTable[ 1 + Dest[ i ] ];
end;
end;
I don't think you need 128 bit math..
Good luck!