Go中的索引突然超出范围

Question

I am trying to implement an algorithm to find all primes below a certain limit. However, when the limit reaches 46350 i suddenly get an out of range error message:

panic: runtime error: index out of range

goroutine 1 [running]:
main.main()
    /tmpfs/gosandbox-433...fd004/prog.go:16 +0x1a8

Any help to point me to what is wrong here is appreciated (and were does this magic number 46350 come from?).

To reproduce drop the following code into googles sandbox and uncomment limit++ (or use this link):

package main

func main() {
    limit := 46349
    //limit++
    sieved_numbers := make([]bool, limit)
    var j = 0
    var i = 2

    for ; i < limit; i++ {
        if !sieved_numbers[i] {
            for j = i * i; j < limit;j += i {
                sieved_numbers[j] = true
            }
        }
    }
}

Answer 1

Because when i == 46349, j = i * i overflows and you're left with a negative number. The loop condition is still true, but it's outside the boundaries of the array, so you get a panic.

Add a fmt.Println(i, j) as the first statement in your nested loop, and run it on your local machine (it'll time out on the sandbox) and you'll see it happen.