如何计算逆模量 [英] how to calculate reverse modulus

问题描述

现在我有一个公式:

int a = 53, x = 53, length = 62, result;
result = (a + x) % length;

但是如果我已经知道结果，如何计算反向模量以获得最小的"x"

but how to calculate reverse modulus to get the smallest "x" if I known result already

(53 + x) % 62 = 44
//how to get x

我的意思是求x的公式或逻辑是什么

i mean what's the formula or logic to get x

推荐答案

private int ReverseModulus(int div, int a, int remainder)
{
   if(remainder >= div)
      throw new ArgumentException("Remainder cannot be greater than or equal to divisor");
   if(a < remainder)
      return remainder - a;
   return div + remainder - a;
}

例如:

// (53 + x) % 62 = 44
var res = ReverseModulus(62,53,44); // res = 53

// (2 + x) % 8 = 3
var res = ReverseModulus(8,2,3); // res = 1

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