英文:
Golang BigInt division
问题
我有一个关于函数的问题，我不明白为什么会发生这种情况。问题是：我有一个很大的数字，但是当我尝试进行一些除法运算时，结果都是零。
代码如下：
for {
fmt.Println("number is", number)
key := number.Mod(number, big.NewInt(10))
fmt.Println("key", key)
first := new(big.Int).Div(number, big.NewInt(10))
fmt.Println("first", first)
number = first
fmt.Println(number)
// number = 0 always as a fisrt variable too
...
}
退出的示例：
number is 6689502913449127057588118054090372586752746333138029810295671352301633557244962989366874165271984981308157637893214090552534408589408121859898481114389650005964960521256960000000000000000000000000000
key 0
first 0
0
数字获取正确，Mod 操作似乎也正确。但是 Div 操作不正确。问题出在哪里？如何计算大数的基本除法运算？
英文:
I have a problem with function and i don't understand why it happen. The problem is: i have a big number, but when i'm trying to make some operations of division - I have zeros.
The code is:
for {
fmt.Println("number is", number)
// key := number % 10
key := number.Mod(number, big.NewInt(10))
fmt.Println("key", key)
// number = number / 10
first := new(big.Int).Div(number, big.NewInt(10))
fmt.Println("first ", first)
number = first
fmt.Println(number) //number = 0 always as a fisrt variable too
... }
The example of exit is:
number is 6689502913449127057588118054090372586752746333138029810295671352301633557244962989366874165271984981308157637893214090552534408589408121859898481114389650005964960521256960000000000000000000000000000
key 0
first 0
0
Number is getting on correnctly, Mod operation is seems correctly too. Div operation is not. What the point is? How can i calculate basic divisions of big numbers?
答案1
得分: 2
问题出在这一行代码上：
key := number.Mod(number, big.NewInt(10))
你调用了number.Mod()，它是Int.Mod()，它会修改接收者number，将其设置为模数0，所以在这之后number将变为零。
你需要使用一个新的big.Int，就像你在Div()操作中使用的那样：
key := new(big.Int).Mod(number, big.NewInt(10))
在Go Playground上试一试。
还要注意，有一个Int.DivMod()可以同时执行这两个操作（Div()和Mod()）。
此外，为了加快循环速度，你应该创建并重复使用*big.Int值，而不是在每次迭代中创建并丢弃它们。最简单的方法是创建并重复使用10：
var ten = big.NewInt(10)
还要创建并重复使用模数和除法结果的值。
英文:
The problem is this line:
key := number.Mod(number, big.NewInt(10))
You call number.Mod() which is Int.Mod() which modifies the receiver which is number, it sets it to the modulus which is 0, so after this number will be zeroed.
You have to use a new big.Int, just as you used for the Div() operation:
key := new(big.Int).Mod(number, big.NewInt(10))
Try it on the Go Playground.
Also note that there is Int.DivMod() which performs both these 2 operations (Div() and Mod()).
Also note that to speed up your loop, you should create and reuse *big.Int values, and not create and throw them away in each iteration. The most trivial is to create and reuse 10:
var ten = big.NewInt(10)
Also create and reuse values for the mod and div results.
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