Hi, I'm trying to convert Rijndael encryption method from TPLockBox to Lazarus/FPC.

While converting the code, I found this routine in Assembler. I'm wondering if somebody can help me convert this to Pascal?.

Here's the routine:

procedure XorMemPrim(var Mem1; const Mem2; Count : Cardinal); register;
asm
push esi
push edi

mov esi, eax //esi = Mem1
mov edi, edx //edi = Mem2

push ecx //save byte count
shr ecx, 2 //convert to dwords
jz @Continue

cld
@Loop1: //xor dwords at a time
mov eax, [edi]
xor [esi], eax
add esi, 4
add edi, 4
dec ecx
jnz @Loop1

@Continue: //handle remaining bytes (3 or less) pop ecx
and ecx, 3
jz @Done

@Loop2: //xor remaining bytes
mov al, [edi]
xor [esi], al
inc esi
inc edi
dec ecx
jnz @Loop2

@Done:
pop edi
pop esi
end;

Thanks in advance,

push esi // move register esi to the top of the stack pop esi // get the top of the stack and put into esi mov esi, eax // esi := eax
shr ecx, 2 // ecx shr 2 (shift right)
the same for and, xor, etc
jz // GOTO = jump if zero (if the result of last command is zero) jnz // GOTO = jump if not zero
add esi, 4 // esi := esi + 4
dec ecx // Dec(ecx)

Procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal);
Var i:integer;
  p1,p2:pointer;
Begin
;
;
for i:=1 to count div 4 do
  begin
  pdword(p1)^:=pdword(p1)^ xor pdword(p2)^;
  p1:=p1+4;
  p2:=p2+4;
  end;
For i:=1 to count mod 4 do
  begin
  pbyte(p1)^:=pbyte(p1)^ xor pbyte(p2)^;
  p1:=p1+1;
  p2:=p2+1;
  end;
End;

Ludo

Wow!, that was fast. Thanks Ludo, I'll try it.

Hello Lazarus-List,

Tuesday, September 13, 2011, 2:42:25 PM, you wrote:

LMR> While converting the code, I found this routine in Assembler. I'm LMR> wondering if somebody can help me convert this to Pascal?. LMR> Here's the routine:

Basically:

LMR> procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal);
procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal);
var
  c: PtrUint;
begin
  for c:=0 to Count-1 do
  begin
    PBYTE(Mem1)[c]^:=PBYTE(Mem1)[c]^ xor PBYTE(Mem2)[c]^;
  end;
end;

Syntax not checked.

Ludo, I did a quick comparison of the results against the Delphi 7 counterpart and the doesn't match.

Also, I tried to compile this in Delphi and I got "Ordinal type
required" on "p1 := P1 + 4". How can avoid this issue?.

Should have told it was for delphi also:

Procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal); Var
i:integer;
  p1,p2:pointer;
Begin
;
;
for i:=1 to count div 4 do
  begin
  pdword(p1)^:=pdword(p1)^ xor pdword(p2)^;
  p1:=pointer(cardinal(p1)+4);
  p2:=pointer(cardinal(p2)+4);
  end;
For i:=1 to count mod 4 do
  begin
  pbyte(p1)^:=pbyte(p1)^ xor pbyte(p2)^;
  p1:=pointer(cardinal(p1)+1);
  p2:=pointer(cardinal(p2)+1);
  end;
End;

I compared the original and above in D6 and the result is the same. The simplistic test program used:

procedure TForm1.FormCreate(Sender: TObject);
var s,s2,s3:string;
i:integer;
begin
  s:='abcdefghij';
  s2:='bcdefghijk';
  XorMemPrim2(s[1],s2[1],length(s2));
  s3:='';
  for i:=1 to length(s2) do
    s3:=s3+inttohex(ord(s[i]),2);
  label1.Caption:=s3;
  s:='abcdefghij';
  s2:='bcdefghijk';
  XorMemPrim(s[1],s2[1],length(s2));
  s3:='';
  for i:=1 to length(s2) do
    s3:=s3+inttohex(ord(s[i]),2);
  label2.Caption:=s3;
end;

BTW. Use PtrUint instead of cardinal if you want to port this to 64 bits. But then it won't compile on Delphi anymore.

Ludo

Well, no, it won't work on Delphi. I just wanted to compare the results between Lazarus and Delphi.

You are forgiven ;)

You could have compared also with fpc on i386. Change

	procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal);
register;

into

	{$asmmode intel}
	procedure XorMemPrim(var Mem1;  const Mem2;  Count : Cardinal);
register;assembler;

and the assembler routine works also in fpc.

Ludo

Ludo, thank you very much!. Now everything is working wonderfully on Lazarus.

Or simply change to mode Delphi for delphi compat code?