汇编实验

C/C++中调用汇编的函数

汇编实现搜索的IndexOf函数
对应第十基础篇

IndexOf.asm

.586
.model flat, C

IndexOf PROTO,
	searchVal: DWORD, arrayPtr: DWORD, count: DWORD

.code
IndexOf PROC USES ecx esi edi,
	searchVal:DWORD, arrayPtr:DWORD, count:DWORD
;
;对32位整数数组执行线性搜索,
;EAX返回该数值的索引位置，否则返回-1
;--------------------------------------
	NOT_FOUND = -1

	mov eax, searchVal
	mov ecx, count
	mov esi, arrayPtr
	mov edi, 0
L1:
	cmp [esi+edi*4], eax
	je found
	inc edi
	loop L1
NotFound:
	mov eax, NOT_FOUND
	jmp short Exit

Found:
	mov eax, edi
Exit:
	ret
IndexOf ENDP
END

C++中调用该函数

main.cpp

#include <iostream>
#include <time.h>

extern "C" long IndexOf(long n, long array[], unsigned count);
using namespace std;
int main()
{
	const unsigned ARRAY_SIZE = 100;
	const unsigned LOOP_SIZE = 10;
	const char* boolstr[] = { "false", "true" };

	long array[ARRAY_SIZE];
	for (unsigned i = 0; i < ARRAY_SIZE; i++){
		array[i] = rand();
	}
	long searchVal;
	time_t startTime, endTime;
	cout << "Enter an integer value to find: ";
	cin >> searchVal;
	cout << "Please wait......\n";

	//测试汇编函数
	time(&startTime);
	int count = 0;

	for (unsigned i = 0; i < LOOP_SIZE; i++){
		count = IndexOf(searchVal, array, ARRAY_SIZE);
	}
	bool found = (count != -1);

	time(&endTime);
	cout << "Elapsed ASM time: " << long(endTime - startTime)
		 << " seconds. Found = " << boolstr[found] << endl;

	return 0;
}

好了，我们的代码就绪了，那，咋链接起来呢？
配置如下：
右键汇编的文件

打开属性页
命令行填写：ml /c /coff %(fileName).asm
输出填写：%(fileName).obj;%(OutPuts)

一个C的代码

int sumarray(int array[], int count){
	int i;
	int sum=0;
	for(i=0;i<count;i++){
		sum+=array[i];
	}
	return sum;
}

汇编代码如下：

sumarray:
 push        ebp  
 mov         ebp,esp  
 sub         esp,0D8h  
 push        ebx  
 push        esi  
 push        edi  
 lea         edi,[ebp-0D8h]  
 mov         ecx,36h  
 mov         eax,0CCCCCCCCh  
 rep stos    dword ptr es:[edi]  
 mov         ecx,offset _CAC8CD7F_consoleapplication2@cpp (013DC002h)  
 call        @__CheckForDebuggerJustMyCode@4 (013D1208h)  
 mov         dword ptr [sum],0  
 mov         dword ptr [i],0  
 jmp         sumarray+41h (013D1731h)  
 mov         eax,dword ptr [i]  
 add         eax,1  
 mov         dword ptr [i],eax  
 mov         eax,dword ptr [i]  
 cmp         eax,dword ptr [count]  
 jge         sumarray+5Ah (013D174Ah)  
 mov         eax,dword ptr [i]  
 mov         ecx,dword ptr [array]  
 mov         edx,dword ptr [sum]  
 add         edx,dword ptr [ecx+eax*4]  
 mov         dword ptr [sum],edx  
 jmp         sumarray+38h (013D1728h)  
 mov         eax,dword ptr [sum]  
 pop         edi  
 pop         esi  
 pop         ebx  
 add         esp,0D8h  
 cmp         ebp,esp  
 call        __RTC_CheckEsp (013D1212h)  
 mov         esp,ebp  
 pop         ebp  
 ret

调试方法:
调试 -> 右键 ->转到反汇编(go to disassembly)
注意：需要在设置里勾选一项：启用地址级调试
工具菜单 -> 选项 -> 调试