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How exactly does the x86 LOOP instruction work?

            mov    ecx, 16
looptop:    .
            .
            .
            loop looptop

How many times will this cycle run?

What happens if you ecx = 0get started? Does the loopjump or fall in this case?

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loopjust like dec ecx / jnzexcept that it does not set flags .

This is like the lower part do{} while(--ecx != 0);in C. If execution enters cycle c ecx = 0, a cyclic transition means that the cycle will execute 2 ^ 32 times. (Or 2 ^ 64 times in 64-bit mode because it uses RCX).

Unlike rep movsb/stosb/etc., it does not check ECX = 0 before decreasing, but only after.

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Source: https://habr.com/ru/post/1688744/

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