add mobius command

cmd/mobius.go

@@ -0,0 +1,97 @@
+/*
+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 cmd
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var mobiusN uint
+
+func mobiusSieve(n uint) chan int {
+	sieve := make([]int, n)
+	for i := 0; i < int(n); i++ {
+		sieve[i] = i
+	}
+
+	ch := make(chan int)
+	go func() {
+		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
+			}
+		}
+
+		close(ch)
+	}()
+
+	return ch
+}
+
+func mobius(cmd *cobra.Command, args []string) {
+	ch := mobiusSieve(mobiusN)
+	for i := 0; ; i++ {
+		v, ok := <-ch
+		if !ok {
+			break
+		}
+
+		if i == 0 {
+			continue
+		}
+
+		fmt.Println(v)
+	}
+}
+
+// mobiusCmd represents the mobius command
+var mobiusCmd = &cobra.Command{
+	Use:   "mobius",
+	Short: "Compute the Möbius function for all numbers less than n",
+	Long:  `Compute the Möbius function for all numbers less than n.`,
+	Run:   mobius,
+}
+
+func init() {
+	sieveCmd.AddCommand(mobiusCmd)
+
+	// Here you will define your flags and configuration settings.
+
+	// Cobra supports Persistent Flags which will work for this command
+	// and all subcommands, e.g.:
+	// mobiusCmd.PersistentFlags().String("foo", "", "A help for foo")
+
+	// Cobra supports local flags which will only run when this command
+	// is called directly, e.g.:
+	// mobiusCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	mobiusCmd.Flags().UintVarP(&mobiusN, "limit", "n", 0, "upper limit")
+	mobiusCmd.MarkFlagRequired("limit")
+}