いいアルゴリズムっていうか小技を教えて

>>123
　判らないといわれると　余計にパスカル書きたくなる

type TaBYTE= array [0..2] of BYTE;
type TPaBYTE= ^TaBYTE;
procedure BlendProc(src,dst,back:TPaBYTE ; ByteSize,ra,rb:Integer );
var H,L,i:Integer;
var s:^Integer absolute src;
var d:^Integer absolute dst;
var b:^Integer absolute back;
begin
while ByteSize>=4 do begin
　H:=　 ((s^ SHR 8) AND $00FF00FF)*ra;
　L:=　　(s^　　　　AND $00FF00FF)*ra;
　inc(s);
　H:=H+ ((d^ SHR 8) AND $00FF00FF)*rb;
　L:=L+　(d^　　　　AND $00FF00FF)*rb;
　b^:= (H AND $FF00FF00) OR ((L SHR 8) AND $00FF00FF);
　inc(d);
　inc(b);
　dec(ByteSize,4);
end;
for i:=0 to ByteSize-1 do begin
　 back^[i] :=(src^[i]*ra +dst^[i]*rb) shr 8;
end;
end;