带模ARM的随机数 [英] Random number with modulo ARM

问题描述

我正在对ARM中的数字游戏进行猜测，以了解更多信息.但是我对随机数的产生感到困惑...我调用rand()，但是我不知道如何做模100来生成0-100范围内的数字.我认为ARM中没有模数，并且和r0，r0，#100"不是很随意...

I'm coding a guess the number game in ARM to learn more about it. But i'm stuck at the random number generation... I call rand() but I don't know how to do the modulo 100 to generate a number in the range 0-100. I don't think there is modulo in ARM and "and r0, r0, #100" is not very random...

这是伪随机数生成的开始:

Here is the start of the pseudo random number generation :

mov r0, #0
bl time
bl srand
bl rand

推荐答案

仅当您感兴趣的其余部分来自除法的幂为2时，AND才起作用.您可以做的一件事是改用一个这样的值的100.

ANDs only work if the remainder you are interested in comes from the division with a power of 2. One thing you could do would be to use one such value instead of 100.

一种替代方法是只使用余数定理:

An alternative would be just to use the remainder theorem:

a％100 = a-(100 * int(a/100))

这也是gcc的功能(尽管它实际上避免了用幸运).

This is what gcc does as well (though it avoids actually dividing with 100 by something called reciprocal multiplication; if your ARM supports integer divide instructions, though, you're lucky).

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