mathtools/cmd/gcd.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"
	"log"
	"math/big"

	"github.com/spf13/cobra"
)

var extended bool

func computeBezouts(bezouts []big.Int, x, y *big.Int) {
	for i, b := range bezouts {
		if i == len(bezouts)-1 {
			bezouts[i].Set(y)
		} else {
			bezouts[i].Mul(&b, x)
		}
	}
}

func gcd(cmd *cobra.Command, args []string) {
	x := new(big.Int)
	y := new(big.Int)
	z := new(big.Int)
	w := new(big.Int)

	bezouts := make([]big.Int, len(args))

	for i, s := range args {
		_, ok := w.SetString(s, 10)
		if !ok {
			log.Fatal("invalid input " + s)
		}

		z.GCD(x, y, z, w)

		if extended {
			computeBezouts(bezouts[:i+1], x, y)
		}
	}

	fmt.Print(z)
	if extended {
		for _, b := range bezouts {
			fmt.Printf(" %s", &b)
		}
	}
	fmt.Println()
}

// gcdCmd represents the gcd command
var gcdCmd = &cobra.Command{
	Use:   "gcd N N [N ...]",
	Short: "Compute the greatest common denominator of a set of numbers",
	Long:  `Compute the greatest common denominator of a set of numbers.`,
	Args:  cobra.MinimumNArgs(2),
	Run:   gcd,
}

func init() {
	rootCmd.AddCommand(gcdCmd)

	// Here you will define your flags and configuration settings.

	// Cobra supports Persistent Flags which will work for this command
	// and all subcommands, e.g.:
	// gcdCmd.PersistentFlags().String("foo", "", "A help for foo")

	// Cobra supports local flags which will only run when this command
	// is called directly, e.g.:
	// gcdCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")

	gcdCmd.Flags().BoolVarP(&extended, "extended", "e", false, "also compute the Bezout coefficients")
}