big.asm

可以进行无限制的整数计算

	.386P
.model FLAT
.code
_MemCpy   proc    near
        push    ebp
        mov     ebp,esp

		mov ecx, [ebp+16]   ;n
		jecxz to_end;	

		;保存方向标志
		pushf	
		
		mov edi,[ebp+8]
		mov esi, [ebp+12]
		cmp edi, esi
		jbe to_up		;dst <= src;
		
		mov eax, ecx
		shl eax, 2
		add eax, esi
		cmp edi, eax
		jae to_up		;dst >= src+4n
		
		;down
		mov eax, ecx
		dec eax
		shl eax, 2
		add edi, eax
		add esi, eax
		std
		jmp to_mov
to_up:
		cld
to_mov:
		rep movsd
		popf
to_end:
		pop ebp
        ret
_MemCpy endp
        end