mathtools/cmd/jacobi.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 cmd

import (
	"fmt"
	"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 {
		cobra.CheckErr("invalid input " + a)
	}

	y, ok := new(big.Int).SetString(n, 10)
	if !ok {
		cobra.CheckErr("invalid input " + n)
	}

	mod := big.NewInt(2)
	mod.Mod(y, mod)
	if mod.Cmp(big.NewInt(0)) == 0 {
		cobra.CheckErr("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")
}