mathtools/internal/lib/mobius.go

/*
Copyright © 2025 filifa

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package lib

/*
MobiusSieve computes mobius(k) for k=1 to n, where mobius is the Mobius function.
*/
func MobiusSieve(n uint, buflen uint) chan int {
	sieve := make([]int, n)
	for i := 0; i < int(n); i++ {
		sieve[i] = i
	}

	ch := make(chan int, buflen)
	go func() {
		defer close(ch)
		for i := 0; i < int(n); i++ {
			if i == 0 || i == 1 || sieve[i] != i {
				ch <- sieve[i]
				continue
			}

			ch <- -1

			for j := 2 * i; j < int(n); j += i {
				if j%(i*i) == 0 {
					sieve[j] = 0
				}

				sieve[j] /= -i
			}
		}
	}()

	return ch
}