Python code to Delphi 7 conversion: endianess-CodePudding

I am trying to convert this code to Delphi 7. In Python it converts hex bytes to big endian:

keydata=[0,0,0,0,0,0,0,0]
for i in range(0,len(data),4):
 Keydata[i//4]=unpack(">I",data[i:i 4])[0]

My Delphi code so far:

Var
Keydata:array of integer;

Setlength(keydata,8);
While i <= Length(data)-1 do begin
Move(data[i], keydata[i div 4], 4);
Inc(i,4);
End;

What is the correct way of converting to big endian in Delphi?

CodePudding user response：

You're almost there, except for the actual endianess reverse. Consider doing that part on your own by exchanging each byte "manually":

var
  keydata: Array of Byte;  // Octets = 8bit per value; Integer would be 32bit
  i: Integer;  // Going through all bytes of the array, 4 at once
  first, second: Byte;  // Temporary storage
begin
  SetLength( keydata, 8 );
  for i:= 0 to 7 do keydata[i]:= i;  // Example: the array is now [0, 1, 2, 3, 4, 5, 6, 7]

  i:= 0;  // Arrays start with index [0]
  while i< Length( keydata ) do begin
    first:= keydata[i];
    second:= keydata[i  1];
    keydata[i]:= keydata[i  3];  // 1st byte gets overwritten
    keydata[i  1]:= keydata[i  2];
    keydata[i  2]:= second;
    keydata[i  3]:= first;  // Remembering the 1st byte

    Inc( i, 4 );  // Next 4 bytes
  end;

  // keydata should now be [3, 2, 1, 0, 7, 6, 5, 4]
end;

This is a rather educational example. See also how to convert big-endian numbers to native numbers delphi. Indenting Pascal code is not mandatory, but it improves reading a lot.