eax, ebx, ecx and so on are actually registers, which can be seen as "hardware" variables, somewhat similar to higher level-language's variables. Registers can be used in your software …

2016年5月12日 · If the ECX register is zero then the repe cmpsb is not executed at all. This means that the following setb and seta instructions would produce garbage! Thus the …

2012年3月22日 · as we know, the loop X instruction is going over X until ECX = 0. My question - What the loop instruction do first: decrement the ECX, or check if ECX == 0. Meaning, what of …

2012年9月14日 · ecx is a x86 CPU register, which can hold a value of a certain amount of bits (32 or 64 (called rcx then) on modern x86 CPU's). The call stack is divided into stack frames . …

imul also has an immediate form: imul ecx, ebx, 1234 does ecx = ebx * 1234. Many assemblers will accept imul ecx, 1234 as short-hand for imul ecx, ecx, 1234 . These 32x32 => 32-bit forms …

2017年3月19日 · The disadvantage of loop is that it's slower than the equivalent sub ecx,1; jnz start_of_loop. The advantage of loop is that it uses less instruction bytes. Think of it as a code …

2011年7月24日 · mov ecx, N jmp bottom top: BODY dec ecx bottom: cmp ecx, 0 jne top Now we still do N conditional jumps but we only do ONE unconditional jump. A small savings but it just …

2016年11月25日 · ECX: "Extended Counter" - often used for loop and string operations, as well as for storing function arguments. EDX: "Extended Data" - often used for I/O operations and …

2014年6月10日 · ecx was the count register which held a loop counter; edx was the data register which you could use for I/O port access; edi was the destination index register which pointed …

2017年10月23日 · Unlike rep movsb/stosb/etc., it doesn't check for ECX=0 before decrementing, only after 1. The address-size determines whether it uses CX, ECX, or RCX. So in 64-bit code, …