简单反汇编之狐狸吃兔子算法

  今天拿狐狸吃兔子算法反了一下，特此坐下记录，算法源码：

http://blog.youkuaiyun.com/ms2146/archive/2009/12/25/5073360.aspx

 

Release版本反汇编分析：

00401000 /$ 83EC 2C SUB ESP,2C //开辟了11个堆栈空间 00401003 |. 33C0 XOR EAX,EAX 00401005 |. 56 PUSH ESI 00401006 |. 57 PUSH EDI 00401007 |. 894424 08 MOV DWORD PTR SS:[ESP+8],EAX 0040100B |. 894424 0C MOV DWORD PTR SS:[ESP+C],EAX 0040100F |. 894424 10 MOV DWORD PTR SS:[ESP+10],EAX 00401013 |. 894424 14 MOV DWORD PTR SS:[ESP+14],EAX 00401017 |. 894424 18 MOV DWORD PTR SS:[ESP+18],EAX 0040101B |. 894424 1C MOV DWORD PTR SS:[ESP+1C],EAX 0040101F |. 894424 20 MOV DWORD PTR SS:[ESP+20],EAX 00401023 |. 894424 24 MOV DWORD PTR SS:[ESP+24],EAX 00401027 |. 894424 28 MOV DWORD PTR SS:[ESP+28],EAX 0040102B |. 894424 2C MOV DWORD PTR SS:[ESP+2C],EAX 0040102F |. 894424 30 MOV DWORD PTR SS:[ESP+30],EAX //给前面开辟的11个堆栈空间赋值为eax=0; 00401033 |. 33C9 XOR ECX,ECX //ecx清零 00401035 |. BE E8030000 MOV ESI,3E8 //esi赋值1000 0040103A |> 41 /INC ECX //ecx自增1 0040103B |. 03C1 |ADD EAX,ECX //eax=eax+ecx 0040103D |. 83F8 0A |CMP EAX,0A //eax和10比较 00401040 |. 7E 0A |JLE SHORT sftest.0040104C //小于等于跳转到sftest.0040104C 00401042 |. 99 |CDQ //将edx至eax的符号位相同 00401043 |. BF 0A000000 |MOV EDI,0A //edi赋值10 00401048 |. F7FF |IDIV EDI //eax/10 0040104A |. 8BC2 |MOV EAX,EDX //取余给eax 0040104C |> 8B7C84 08 |MOV EDI,DWORD PTR SS:[ESP+EAX*4+8] //获取ESP+EAX*4+8可以看出每次改变的是eax,这里的eax是索引,后面乘4是因为以4字节为单位,加8是因为上面分配的数组是从esp+8开始的 00401050 |. 47 |INC EDI //edi自增1 00401051 |. 4E |DEC ESI //循环变量esi总共循环1000次，这里是减一 00401052 |. 897C84 08 |MOV DWORD PTR SS:[ESP+EAX*4+8],EDI //将计算好的edi在重复放入eax索引处的堆栈 00401056 |.^ 75 E2 /JNZ SHORT sftest.0040103A //跳转上去继续循环 00401058 |. 8D7424 0C LEA ESI,DWORD PTR SS:[ESP+C] //取数组第一个元素偏移 0040105C |. BF 0A000000 MOV EDI,0A 00401061 |> 8B06 /MOV EAX,DWORD PTR DS:[ESI] //获取数组数据 00401063 |. 50 |PUSH EAX 00401064 |. 68 30704000 |PUSH sftest.00407030 ; ASCII "%d/n" 00401069 |. E8 22000000 |CALL sftest.00401090 0040106E |. 83C4 08 |ADD ESP,8 00401071 |. 83C6 04 |ADD ESI,4 00401074 |. 4F |DEC EDI 00401075 |.^ 75 EA /JNZ SHORT sftest.00401061 00401077 |. 5F POP EDI 00401078 |. 5E POP ESI 00401079 |. 83C4 2C ADD ESP,2C //清理堆栈 0040107C /. C3 RETN

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