在delphi中合并两个字节

Question

Provided that I have two bytes variables in Delphi:

var 
    b1,b2,result:byte;
begin
    b1:=$05;
    b2:=$04;
    result:=??? // $54
end;

How would I then combine the two to produce a byte of value $54 ?

Answer 1

The most trivial way is

result := b1 * $10 + b2

"Advanced" way:

result := b1 shl 4 + b2

Answer 2

The best way would be to:

interface

function combine(a,b: integer): integer; inline;  //allows inlining in other units

implementation

function combine(a,b: cardinal): cardinal; inline;
begin
  Assert((a <= $f));
  Assert((b <= $f));
  Result:= a * 16 + b;
end;

Working with byte registers slows down the processor due to partial register stalls .
The asserts will get eliminated in release mode.

If performance matters never use anything but integers (or cardinals).

I have no idea why people are talking about VMT's or dll's. It's a simple inline method that does not even generate a call.