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Miscellaneous Forums => Archive => Topic started by: mav on 2005-05-19 22:47:52

Title: Cosmo Canyon save patch
Post by: mav on 2005-05-19 22:47:52

I figured that it would be cool to develop patch for Cosmo Canyon so you mustn't see the animation. It would be a simple patch to change plot progression variable (before going to Bugenhaggen it's 0xD5 and after - 0xED). Unfortunetly, I'm not that good in C++ and I'm writing in Delphi, and I have problem with checksum function:

Qhimm's code:

Code: [Select]

int CFF7File::Checksum( char* b )
{
	int i = 0, t, d;
	long r = 0xFFFF, len = 4336;
	long pbit = 0x8000;

	while( len-- ) {
		t = b[i++];
		r ^= t << 8;
		for(d=0;d<8;d++) {
			if( r & pbit )
				r = ( r << 1 ) ^ 0x1021;
			else
				r <<= 1;
		}
		r &= ( 1 << 16 ) - 1;
	}
	return ~r;
}

My code:

Code: [Select]

  var i, t, d, r, len, pbit: integer;
  content: array of char;
    i := 0;
    while (len >= 0) do begin
      len := len - 1;
      i := i + 1;
      t := ord(content[i]);
      r := r xor (t shl 8);
      for d := 0 to 7 do begin
        if(r and pbit)=0 then
          r := ( r shl 1 ) xor $1021
        else
          r := r shl 1;
        r := r and ((1 shl 16) - 1);
      end;
    end;

Could someone point me what I have done wrong ? Program calculates something, but it's diffrent from the original. Help apprieciated :).

Title: Cosmo Canyon save patch
Post by: Synergy Blades on 2005-05-19 23:00:33

This bit made me wonder:

Code: [Select]

if( r & pbit ) 
r = ( r << 1 ) ^ 0x1021;

So the r = ( r << 1 ) ^ 0x1021 is run if (r & pbit) is not zero, where as looking at yours you're comparing (r & pbit) to see if it is zero:

Code: [Select]


if(r and pbit)=0 then 
r := ( r shl 1 ) xor $1021

Oh and the obvious question since I haven't used Delphi, you have given a value to those variable such as len, p?

Title: Cosmo Canyon save patch
Post by: mav on 2005-05-19 23:09:32

Thanks for posting. Tried this, still, no luck... :-?

Title: Cosmo Canyon save patch
Post by: Synergy Blades on 2005-05-19 23:24:14

The only other thing I thought about was that Qhimm uses longs for some variables where you use integers. Not sure what range/size/representation Delphi uses for an integer, but if it's different I thought it might be a problem since you're bitshifting r, so if they're of different sizes for example you would end up with a different result.

Anyway, wait til Qhimm arrives (or Ficedula, if you're lucky :wink: )

Title: Cosmo Canyon save patch
Post by: Qhimm on 2005-05-20 04:31:18

Here's what I can see from looking at it (mostly covered by previous posts):

God, I wrote ugly code back then.
You don't seem to be initializing the variables r, len and pbit.
You are pre-incrementing i (before indexing the data) instead of post-incrementing. IIRC Delphi dynamic arrays are zero-based, so this is probably incorrect.
You're testing for (r and pbit) = 0, which is the opposite condition of my code. It should be tested for non-zero.
I don't think the constriction to 16-bit data size is needed inside the loop, it could probably be moved out to the return statement (ineffective code on my part, not yours).
You are not inverting the checksum before returning (i.e. r := r xor $ffff)

Code: [Select]

  var i, t, d, r, len, pbit: integer;
  content: array of char;
    i := 0;
    r := $ffff;
    len := 4336;
    while (len >= 0) do begin
      len := len - 1;
      t := ord(content[i]);
      i := i + 1;
      r := r xor (t shl 8);
      for d := 0 to 7 do begin
        if (r and pbit) = 0 then
          r := r shl 1
        else
          r := ( r shl 1 ) xor $1021;
      end;
    end;
    r := (r xor $ffff) and $ffff;

Then again as I'm no Delphi expert... I even had to reverse the if clause since I don't know how to test for value non-zero in Delphi. :P

Title: Cosmo Canyon save patch
Post by: mav on 2005-05-24 13:22:22

I've tried this, still, something is wrong. I guess I'll wait for Fice, because he's good at translating C++ -> Delphi ;)