了解MSVS C ++编译器优化

我不明白这段代码中发生了什么。C代码是：

#include <stdio.h>

int main()
{
    const int mul = 100;
    int x;
    printf_s("Input a number\r\n");
    scanf_s("%i", &x);
    printf_s("%i/%i = %i\r\n", x, mul, x / mul);
    return 0;
}

我希望生成的程序集将进行一些简单的移位和加/减运算，但是会有一些魔术常数，例如51EB851Fh，乘法等。这是怎么回事？

; int __cdecl main()
_main proc near

x= dword ptr -8
var_4= dword ptr -4

push    ebp
mov     ebp, esp
sub     esp, 8
mov     eax, ___security_cookie
xor     eax, ebp
mov     [ebp+var_4], eax
push    offset Format   ; "Input a number\r\n"
call    ds:__imp__printf_s
lea     eax, [ebp+x]
push    eax
push    offset aI       ; "%i"
call    ds:__imp__scanf_s
mov     ecx, [ebp+x]
mov     eax, 51EB851Fh
imul    ecx
sar     edx, 5
mov     eax, edx
shr     eax, 1Fh
add     eax, edx
push    eax
push    64h
push    ecx
push    offset aIII     ; "%i/%i = %i\r\n"
call    ds:__imp__printf_s
mov     ecx, [ebp+var_4]
add     esp, 1Ch
xor     ecx, ebp        ; cookie
xor     eax, eax
call    @__security_check_cookie@4 ; __security_check_cookie(x)
mov     esp, ebp
pop     ebp
retn
_main endp