add modular inverse command

cmd/modInverse.go

@@ -0,0 +1,75 @@
+/*
+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 modInverseG string
+var modInverseM string
+
+func modInverse(cmd *cobra.Command, args []string) {
+	g, ok := new(big.Int).SetString(modInverseG, 10)
+	if !ok {
+		cobra.CheckErr("invalid input " + modInverseG)
+	}
+
+	n, ok := new(big.Int).SetString(modInverseM, 10)
+	if !ok {
+		cobra.CheckErr("invalid input " + modInverseM)
+	}
+
+	z := new(big.Int)
+	res := z.ModInverse(g, n)
+	if res == nil {
+		cobra.CheckErr("cannot find a modular inverse: " + modInverseG + " is not relatively prime to modulus " + modInverseM)
+	} else {
+		fmt.Println(z)
+	}
+}
+
+// modInverseCmd represents the modInverse command
+var modInverseCmd = &cobra.Command{
+	Use:   "mod-inverse",
+	Short: "Compute a modular inverse",
+	Long:  `Compute a modular inverse.`,
+	Run:   modInverse,
+}
+
+func init() {
+	rootCmd.AddCommand(modInverseCmd)
+
+	// Here you will define your flags and configuration settings.
+
+	// Cobra supports Persistent Flags which will work for this command
+	// and all subcommands, e.g.:
+	// modInverseCmd.PersistentFlags().String("foo", "", "A help for foo")
+
+	// Cobra supports local flags which will only run when this command
+	// is called directly, e.g.:
+	// modInverseCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
+
+	modInverseCmd.Flags().StringVarP(&modInverseG, "base", "g", "", "integer to compute modular inverse of")
+	modInverseCmd.MarkFlagRequired("base")
+
+	modInverseCmd.Flags().StringVarP(&modInverseM, "modulus", "m", "", "modulus")
+	modInverseCmd.MarkFlagRequired("modulus")
+}