Tau function: Difference between revisions

=={{header|D}}==

{{trans|C++}}

<lang d>import std.stdio;

// See https://en.wikipedia.org/wiki/Divisor_function

uint divisor_count(uint n) {

uint total = 1;

// Deal with powers of 2 first

for (; (n & 1) == 0; n >>= 1) {

++total;

}

// Odd prime factors up to the square root

for (uint p = 3; p * p <= n; p += 2) {

uint count = 1;

for (; n % p == 0; n /= p) {

++count;

}

total *= count;

}

// If n > 1 then it's prime

if (n > 1) {

total *= 2;

}

return total;

}

void main() {

immutable limit = 100;

writeln("Count of divisors for the first ", limit, " positive integers:");

for (uint n = 1; n <= limit; ++n) {

writef("%3d", divisor_count(n));

if (n % 20 == 0) {

writeln;

}

}

}</lang>

{{out}}

<pre>Count of divisors for the first 100 positive integers:

1 2 2 3 2 4 2 4 3 4 2 6 2 4 4 5 2 6 2 6

4 4 2 8 3 4 4 6 2 8 2 6 4 4 4 9 2 4 4 8

2 8 2 6 6 4 2 10 3 6 4 6 2 8 4 8 4 4 2 12

2 4 6 7 4 8 2 6 4 8 2 12 2 4 6 6 4 8 2 10

5 4 2 12 4 4 4 8 2 12 4 6 4 4 4 12 2 6 6 9</pre>