Convert hex str to decimal value in delphi

Question

I've got a problem to convert a string representation of an hex value in integer value with Delphi.

for example:

$FC75B6A9D025CB16 give me 802829546 when i use the function:

Abs(StrToInt64('$FC75B6A9D025CB16'))

but if i use the calc program from Windows, the result is: 18191647110290852630

So my question is: who's right? me, or the calc?

Does anybody already have this kind of problem?

Answer 1

I had to use a Delphi library named "DFF Library" because I work on Delphi6 and the type Uint64 does not exist in this version.
Main page

Here's my code to transform a string of hexadecimal value to a string of decimal value:

You need to add UBigIntsV3 to your uses in your unit.

function StrHexaToUInt64Str(const stringHexadecimal: String): string;
var
  unBigInteger:TInteger;
begin
  unBigInteger:=TInteger.Create;
  try
    // stringHexadecimal parameter is passed without the '$' symbol
    // ex: stringHexadecimal:='FFAA0256' and not '$FFAA0256'
    unBigInteger.AssignHex(stringHexadecimal);
    //the boolean value determine if we want to add the thousand separator or not.
    Result:=unBigInteger.converttoDecimalString(false);
  finally
    unBigInteger.free;
  end;
end;

Answer 2

In fact 802829546 is clearly wrong here.

Calc returns a 64bit unsigned value (18191647110290852630d).

Delphi Int64 type uses highest bit as sign:

Int := StrToInt64('$FC75B6A9D025CB16');
Showmessage(IntToStr(Int));

returns value -255096963418698986 which is correct

If you need to work with values larger than 64bit signed, then check out Arnaud's answer here.

Answer 3

The number is too big to be represented as a signed 64-bit number.

FC75B6A9D025CB16h = 18191647110290852630d

The largest possible signed 64-bit value is

2^63 - 1 = 9223372036854775807

Answer 4

to work with big numbers you need external library for delphi

Large numbers in Pascal (Delphi)