Delphi + Asm TBits类的学习

技术交流,DH讲解. 在D2010的classes中有个TBits类,这个类主要是位操作的. TBits = class
private
FSize: Integer;
FBits: Pointer;
procedure Error;
procedure SetSize(Value: Integer);
procedure SetBit(Index: Integer; Value: Boolean);
function GetBit(Index: Integer): Boolean;
public
destructor Destroy; override;
function OpenBit: Integer;
property Bits[Index: Integer]: Boolean read GetBit write SetBit; default;
property Size: Integer read FSize write SetSize;
end;
这个类没有什么方法,我们看到了property Bits[Index: Integer]: Boolean read GetBit write SetBit; default;这个属性,就是读取和设置某一位的.

那我们看看它是怎么实现的?
//在类中Eax就是Self指针
procedure TBits.SetBit(Index: Integer; Value: Boolean); assembler;
asm
CMP Index,[EAX].FSize //如果Indx>=Size then 扩容
JAE @@Size
@@1: MOV EAX,[EAX].FBits
OR Value,Value
JZ @@2
BTS [EAX],Index //将Eax中第Index位赋值给CF,然后Eax第index位=1;
RET
@@2: BTR [EAX],Index //将Eax中第Index位赋值给CF,然后Eax第index位=0;
RET
@@Size: CMP Index,0 //if index