add jacobi subcommand

cmd/jacobi.go

@@ -0,0 +1,76 @@
+/*
+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"
+	"log"
+	"math/big"
+
+	"github.com/spf13/cobra"
+)
+
+var a string
+var n string
+
+func jacobi(cmd *cobra.Command, args []string) {
+	x, ok := new(big.Int).SetString(a, 10)
+	if !ok {
+		log.Fatal("invalid input " + a)
+	}
+
+	y, ok := new(big.Int).SetString(n, 10)
+	if !ok {
+		log.Fatal("invalid input " + n)
+	}
+
+	mod := big.NewInt(2)
+	mod.Mod(y, mod)
+	if mod.Cmp(big.NewInt(0)) == 0 {
+		log.Fatal("modulus must be odd")
+	}
+
+	z := big.Jacobi(x, y)
+	fmt.Println(z)
+}
+
+// jacobiCmd represents the jacobi command
+var jacobiCmd = &cobra.Command{
+	Use:   "jacobi -a A -n N",
+	Short: "Compute the Jacobi symbol",
+	Long:  `Compute the Jacobi symbol (a | n).`,
+	Run:   jacobi,
+}
+
+func init() {
+	rootCmd.AddCommand(jacobiCmd)
+
+	// Here you will define your flags and configuration settings.
+
+	// Cobra supports Persistent Flags which will work for this command
+	// and all subcommands, e.g.:
+	// jacobiCmd.PersistentFlags().String("foo", "", "A help for foo")
+
+	// Cobra supports local flags which will only run when this command
+	// is called directly, e.g.:
+	// jacobiCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	jacobiCmd.Flags().StringVarP(&a, "residue", "a", "", "residue")
+	jacobiCmd.MarkFlagRequired("residue")
+	jacobiCmd.Flags().StringVarP(&n, "modulus", "n", "", "modulus")
+	jacobiCmd.MarkFlagRequired("modulus")
+}