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Delphi 3 .  Typecasts

Posted on 1998-05-26
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Last Modified: 2008-03-17
I need to manipulate bits within a single. Under D1 I did it like this...
Delphi won't allow bitwise operations on reals (why not!!) so the single is treated as a longint to do the manipulations, then the resulting bit pattern is treated as a single.
Type
    SType = single;
    LType = longint;
Var
    sing1 : single;
    long1 : longint;

long1 := LType(sing1);  {typecast the single as a longint}

{do the SHR, AND, OR manipulations here}

sing1 := SType(long1);  {longint back to a single}

Under D3 I get a compiler error "invalid typecast".
Can anyone tell me why, and how do I fix it.

Thanks.
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Question by:frog
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6 Comments
 
LVL 1

Expert Comment

by:Socrates050697
ID: 1347922
Instead of typecasting, use the ROUND() function to convert the single to an integer. Also  you don't need to typecast to go the other way.

eg


    Var
        sing1 : single;
        long1 : longint;

    long1 := Round(sing1);

    {do the SHR, AND, OR manipulations here}

    sing1 := long1;



Socrates
0
 
LVL 3

Expert Comment

by:rickpet
ID: 1347923
Okay...you can't do it directly but you can do it indirectly...pass the address back and forth and manipulate the values of the addresses...

type
  pMyLongInt = ^Integer;
  pMySingle = ^Single;
var
  mySingle: single;
  myLongInt: LongInt;
  ptrMyLongInt : pMyLongInt;
  ptrMySingle: pMySingle;
  myPointer: Pointer;
begin

  mySingle := 2.01;
  myPointer := @mySingle;
  ptrmyLongInt := myPointer;
  myLongInt := ptrmyLongInt^;
  myLongInt := myLongInt SHL 1;
  myPointer := @myLongInt;
  ptrMySingle := myPointer;
  mySingle := ptrMySingle^;
  Label1.Caption := FloatToStr(mySingle);

0
 
LVL 3

Expert Comment

by:rickpet
ID: 1347924
In Delphi 1 you need to change my Type of pMyLongInt to
pMyLongInt = ^LongInt (In 32bit world LongInt = Integer)

Rick
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Author Comment

by:frog
ID: 1347925
Socrates, thanks for your reply but the round() will convert the real to a longint value and data format, it therefore will not preserve the bit pattern of the single which I want to manipulate.

rickpet, thanks for the pointers reminder. I'm sure it will work, I'll do it when I get time.


0
 

Author Comment

by:frog
ID: 1347926
rickpet I'll accept your answer but I don't think there is any way for me to give you the points until you send it as an answer instead of a comment. Is that right?

0
 
LVL 3

Accepted Solution

by:
rickpet earned 100 total points
ID: 1347927
Yup...here's your answer...Thanks...

Rick
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