move sieves to subpackage

internal/lib/sieve/totient.go

@@ -0,0 +1,46 @@
+/*
+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 sieve
+
+/*
+TotientSieve computes totient(k) for k=1 to n, where totient is Euler's totient function. buflen sets the buffer length of the returned channel. Larger buffer lengths can result in better performance at the cost of higher memory usage.
+*/
+func TotientSieve(n uint, buflen uint) chan uint {
+	totients := make([]uint, n)
+	totients[0] = 0
+	totients[1] = 1
+	for i := uint(2); i < n; i++ {
+		totients[i] = i - 1
+	}
+
+	ch := make(chan uint, buflen)
+	go func() {
+		defer close(ch)
+		for i := uint(0); i < n; i++ {
+			ch <- totients[i]
+			if i == 0 || i == 1 || totients[i] != i-1 {
+				continue
+			}
+
+			for j := 2 * i; j < n; j += i {
+				totients[j] -= totients[j] / i
+			}
+		}
+	}()
+
+	return ch
+}