Question

In my program I need to generate array with powers’ (from 0 to 5) sum of numbers from 1 to 100,000.

So I tried to compile this code:

const enum size_t MAX_ARRAY_SIZE = 100_000 + 1;
const enum size_t MAX_POWER_SIZE = 5 + 1;
const enum power_sum = calc_power_sum();

// some unimportant code here

pure ulong[MAX_POWER_SIZE][MAX_ARRAY_SIZE] calc_power_sum() {
    ulong[MAX_POWER_SIZE][MAX_ARRAY_SIZE] power_sum;

    power_sum[0][] = 1;

    foreach (x, ref element; power_sum[1]) {
        element = x;
    }

    foreach (n; 2 .. MAX_POWER_SIZE) {
        foreach (x, ref element; power_sum[n]) {
            element = power_sum[n - 1][x] * power_sum[1][x];
        }
    }


    foreach (ref power; power_sum) {
        foreach (x; 1 .. MAX_ARRAY_SIZE) {
            power[x] += power[x - 1]; // error appears here
        }
    }

    return power_sum;
}

But compiler says:

$ dmd problem.d
problem.d(130): Error: array index 6 is out of bounds [1LU, 2LU, 3LU, 4LU, 5LU, 6LU][0 .. 6]
problem.d(15): called from here: calc_power_sum()

What am I doing wrong?

Answer 1

At first glance looks like you have simply misunderstood array dimension order. You have

ulong[MAX_POWER_SIZE][MAX_ARRAY_SIZE]

and your code assumes directly opposite

ulong[MAX_ARRAY_SIZE][MAX_POWER_SIZE]

Also I am afraid 100 000 may be a bit too much, after above mentioned fix I get an internal compiler error. Works for smaller MAX_ARRAY_SIZE values though.