x86---32汇编(1)---乘除法
最近想优化一下代码的运行速度,笔者就想着汇编的效率比较高,所以就看网上的一些书籍,
练习了一下汇编,乘除法的指令imul和idiv。
代码:
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#include <stdio.h> #include <tchar.h> extern "C" int IntegerMulDive_(int a, int b, int *prod, int *quo, int *rem); int _tmain(int argc, _TCHAR* argv[]) { int a = 21, b = 9; int prod = 0, quo = 0, rem = 0; int rc; rc = IntegerMulDive_(a, b, &prod, &quo, &rem); printf("Input1-a:%4d b:%4d\n", a, b); printf("Output1-rc:%4d prod:%4d\n",rc,prod); printf("quo:%4d rem:%4d\n\n", quo, rem); a = -29; prod = quo = rem = 0; rc = IntegerMulDive_(a, b, &prod, &quo, &rem); printf("Input2-a:%4d b:%4d\n", a, b); printf("Output-2-rc:%4d prod:%4d\n",rc,prod); printf("quo:%4d rem:%4d\n\n", quo, rem); b = 0; prod = quo = rem = 0; rc = IntegerMulDive_(a, b, &prod,&quo, &rem); printf("Input3-a:%4d b:%4d\n", a, b); printf("Output3-rc:%4d prod:%4d\n", rc, prod); printf("quo:%4d rem:%4d\n\n", quo, rem); return 0; }
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.model flat,c .code ; extern "C" int IntegerMulDiv_(int a, int b, int* prod, int* quo, int*rem); ; Description: This function demonstrates use of the imul and idiv ; instructions. It also illustrates pointer usage. ; ; Returns: 0 Error (divisor is zero) ; 1 Success (divisor is zero) ; ; Computes: *prod = a * b; ; *quo = a / b ; *rem = a % b IntegerMulDive_ proc ;Function prolog push ebp mov ebp,esp push ebx ;Make sure the divisor is not zero xor eax,eax ;set error return code mov ecx,[ebp+8] ;ecx='a' mov edx,[ebp+12] ;edx='b' or edx,edx jz InvalidDivisor ;jump if 'b' is zero ;Calulate product and save result imul edx,ecx ;edx='a'*'b' mov ebx,[ebp+16] ;ebx='prod' mov [ebx],edx ;save product ;Calculate quotient and remainder,save results mov eax,ecx ;eax='a' cdq ;edx:eax contains dividend idiv dword ptr [ebp+12] ;eax=quo,edx=rem mov ebx,[ebp+20] ;ebx='quo' mov [ebx],eax ;save quotient mov ebx,[ebp+24] ;ebx='rem' mov [ebx],edx ;save remainder mov eax,1 ;set success return code ;Function epilog InvalidDivisor: pop ebx pop ebp ret IntegerMulDive_ endp end
运行效果: