汇编看不懂(32分)

烂

烂泥

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GUEST, unregistred user!

• 2000-08-31

• #1

demo下DB/bkquery 中的代码看不懂

var
Guard: Integer;
Numbers: Integer;

{ Thread safe increment of Numbers to guarantee the result is unique }

function GetUniqueNumber: Integer;
asm
@@1: MOV EDX,1
XCHG Guard,EDX
OR EDX,EDX
JNZ @@2
MOV EAX,Numbers
INC EAX
MOV Numbers,EAX
MOV Guard,EDX
RET

@@2: PUSH 0
CALL Sleep
JMP @@1
end;

 

A

Another_eYes

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GUEST, unregistred user!

• 2000-08-31

• #2

var
Guard: Integer;
Numbers: Integer;
asm
@@1: MOV EDX,1
XCHG Guard,EDX
OR EDX,EDX
JNZ @@2
MOV EAX,Numbers
INC EAX
MOV Numbers,EAX
MOV Guard,EDX
RET @@2: PUSH 0
CALL Sleep
JMP @@1
end
==> pas代码:
var
EDX: Integer;
Guard: Integer;
Numbers: Integer;
begin
repeat
EDX := Guard;
Guard := 1;
Sleep(0);
until EDX <> 0;
Inc(Numbers);
Guard := EDX;
end;

 

Z

zwhc

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #3

那么在这里使用汇编的好处又是什么呢？
干脆用 pas 代码不行吗？

 

A

Another_eYes

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #4

别问我呀, 问作者去

 

Z

zwhc

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #5

哦，
明白了
谢谢

 

C

coao

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #6

咦，你现在搞汇编呀。

 

烂

烂泥

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #7

to: coao
么啦!

 

S

steve

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-01

• #8

呵呵，死循环啊。

 

Z

zouming

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-05

• #9

解释如下：
function GetUniqueNumber: Integer;
asm //在Pascal中内嵌汇编语言
@@1: MOV EDX,1 //寄存器EDX：=1
XCHG Guard,EDX //交换变量和EDX值
OR EDX,EDX //逻辑或，结果送EDX
JNZ @@2 //不等零则转标号@@2
MOV EAX,Numbers //让EAX：=Numbers
INC EAX //EAX：=EAX+1
MOV Numbers,EAX //Numbers:=EAX
MOV Guard,EDX //Guard:=EDX
RET //跳转
@@2: PUSH 0 //将0压入堆栈
CALL Sleep //进入过程Sleep
JMP @@1 //无条件转到标号@@1
end;

 

烂

烂泥

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-23

• #10

多人接受答案了。

 

S

SNKoala

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-29

• #11

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
高手！佩服！
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

这段代码用于同步读取和设置Numbers变量！！！！
XCHG Guard,EDX

这是至关重要的一句！！！不过不知道要是有多个CPU同时执行，会不会有问题！如果
不是对效率要求特别高，我想还是用临界区等系统提供的方法为妙!

To:steve
不是死循环！

 

S

SNKoala

Unregistered / Unconfirmed

GUEST, unregistred user!

• 2000-09-29

• #12

To:Another_eYes

var
EDX: Integer;
Guard: Integer;
Numbers: Integer;
begin
repeat
EDX := Guard; ///// 1
Guard := 1; ///// 2
Sleep(0);
until EDX <> 0;
Inc(Numbers);
Guard := EDX;
end;

好像改的不对，就算改对了也会有问题——在执行1，2句之间可能会被打断，那就糟了！