lerxst's short answer is going to be right 99% of the time. Just cause I needed a break from hammering out these templates I compiled them both for you and generated the assembly.
Optimizations off MSVC10
Code:
; x += y;
; x /= 10;
mov edx, DWORD PTR _x$[ebp]
add edx, DWORD PTR _y$[ebp]
mov DWORD PTR _x$[ebp], edx
mov eax, DWORD PTR _x$[ebp]
cdq
mov ecx, 10
idiv ecx
mov DWORD PTR _x$[ebp], eax
; x = (x + y) / 10;
mov eax, DWORD PTR _x$[ebp]
add eax, DWORD PTR _y$[ebp]
cdq
mov ecx, 10
idiv ecx
mov DWORD PTR _x$[ebp], eax
Optimizations on MSVC10(/O2)
Code:
; x += y;
; x /= 10;
mov eax, 1717986919
lea ecx, DWORD PTR [edx+edi]
imul ecx
sar edx, 2
mov eax, edx
shr eax, 31
add eax, edx
; x = (x + y) / 10;
mov eax, 1717986919
lea ecx, DWORD PTR [edx+edi]
imul ecx
sar edx, 2
mov eax, edx
shr eax, 31
add eax, edx
With optimizations on they both generate the same code, with them off it's slightly different.
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