Is simple way to convert double value to its bytes representation? I tried using pointers like:
var
double_v:double;
address:^double;
....
double_v:=100;
address:=@double_v;
but every my concepts: how to read thise 8 bytes from address, end with "AV".
Use a variant record
Type
TDoubleAndBytes = Record
case boolean of
false : (dabDouble : Double);
true : (dabBytes : Array [0..7] Of Byte);
end;
Assign the double value to dabDouble and read the bytes through dabBytes
var
myVar : TDoubleAndBytes;
i : integer;
begin
myVar.dabDouble := 100;
for i:=0 to 7 do write(myVar.dabBytes[i]);
double away from an 8 byte boundary. Which will lead to runtime failure for SSE code. For example, x64 floating point. The key, and this is not well understood in my experience, is that packed affects both internal layout, and overall alignment.packed record filler : byte; case boolean...)In XE3 there are record helpers for simple types, TDoubleHelper.
This works:
var
d : Double;
i : Integer;
begin
d := 100.0;
for i := 0 to 7 do
WriteLn(d.Bytes[i]);
end;
In XE2 there is a declaration TDoubleRec, which is an advanced record.
example:
var
dRec : TDoubleRec;
i : Integer;
begin
dRec := 100.0;
for i := 0 to 7 do
WriteLn(dRec.Bytes[i]);
end;
Another common option to access the bytes of a double is to use a typecast:
type
TDoubleAsByteArr = array[0..7] of byte;
var
d : Double;
i : Integer;
begin
d := 100.0;
for i := 0 to 7 do
WriteLn(TDoubleAsByteArr(d)[i]);
end;
Two examples for using of "absolute" ...
Used as function
function GetDoubleByte(MyDouble: Double; Index: Byte): Byte;
var
Bytes: array[0..7] of Byte absolute MyDouble;
begin
Result := Bytes[Index];
end;
procedure TForm1.Button1Click(Sender: TObject);
var
MyDouble:Double;
DoubleBytes:Array[0..7] of Byte absolute MyDouble; // direct local use
begin
MyDouble := 17.123;
ShowMessage(IntToStr(DoubleBytes[0])); // local usage
ShowMessage(IntToStr(GetDoubleByte(MyDouble,0))); // via function call
end;
