From: Felipe Rocha Machado <felipe.jiujitsu@pmail.net>
To: <EarlGlynn>
Subject: Computer Lab Feedback
Date: Thursday, May 06, 1999 7:34 AM

Hello Earl,

I am very glad to write this to you. Your articles and sample programs
helped me a lot (hey! now I've made a component that can show a grayed
version of an image while the mouse is outside it and the original color
version when the mouse is over... without blinking... thank you! :-)...

But, I am not writting only to say hello and thanks! I have a little
feedback to give to you...

Remember the CRC calculator? You've stated the following in the source
code:

"source quote"
// In D3 there is no way to print an unsigned 4-byte integer, so
// some CRC-32 values in decimal may be negative.  In D4, all values
// are unsigned.
//
//  Test         CRC-16             CRC-32
// String     Dec     Hex        Dec       Hex
// -------   -----   ----    ----------  --------
//   abc     38712   9738    -891568579  CADBBE3D  (D3)
//                           3403398717  CADBBE3D  (D4)
//
//   ABC     17697   4521    1551695031  5C7CFCB7  (D3/D4)
"end"

well, It is right. But we forgot that there is the "Integer" type
Currency, that is a 64 bit scaled integer that could do the job for us,
so I write the following routine and voila: we can now print a 32 bit
integer in D3:

function DWORDToStr(v: DWORD): String;
var c: Currency;
begin
  if (High(DWORD) <> 2147483647) or (v >= 0)
  then
    Result := IntToStr(v)
  else begin
    c := 4294967296.0+v; // remember: (4294967296 = 2^32) and v is
negative!
    Result := CurrToStr(c);
  end;
end;

I've changed the source for the CRC calculator to read the following:

procedure TCRCCalc.CRCTextChange(Sender: TObject);
  VAR
    CRC16:  WORD;
    CRC32:  DWORD;
    s    :  STRING;
begin
  s := CRCText.Text;
  CRC16 := 0;          // Could use $FFFF or other initial value
  IF   LENGTH(s) > 0   // Avoid access violation in D4
  THEN CalcCRC16 (Addr(s[1]), LENGTH(s), CRC16);
  CRC16Decimal.Caption := IntToStr(CRC16);
  CRC16Hex.Caption := IntToHex(CRC16,4);

  CRC32 := $FFFFFFFF;   // To match PKZIP
  IF   LENGTH(s) > 0    // Avoid access violation in D4
  THEN CalcCRC32 (Addr(s[1]), LENGTH(s), CRC32);
  CRC32Decimal.Caption := DWORDToStr(CRC32); //IntToStr(CRC32); Now it
prints 3403398717 for 'abc'
  CRC32Hex.Caption := IntToHex(CRC32,8);

end;

Test it yourself, it works (or seems to work...)

Goodbye from your brazillian friend,
        Felipe Rocha Machado
        GPS Tecnologia Ltda.

PS.: May your family keep their patience :-) cause your work is for the
best of us all!