diff --git a/polynomial.js b/polynomial.js
index ad2a899..8f9fc44 100644
--- a/polynomial.js
+++ b/polynomial.js
@@ -8,13 +8,17 @@ class Polynomial {
 
 exports.Class = Polynomial;
 
-function add(p1, p2) {
+function get_mod(p1, p2) {
     let n;
     if (p1.mod !== p2.mod) {
         throw "different modulo"
     } else {
-        n = p1.mod;
+        return p1.mod;
     }
+}
+
+function prepare(p1, p2) {
+    let n = get_mod(p1, p2);
     let len_p1 = p1.coefficients.length;
     let len_p2 = p2.coefficients.length;
     result = new Array(Math.max(len_p1, len_p2)).fill(0);
@@ -23,6 +27,19 @@ function add(p1, p2) {
     } else {
         for (let x = 0; x < len_p2 - len_p1; x++) p1.coefficients.push(0);
     }
+    return {
+        result,
+        n
+    };
+
+}
+
+function add(p1, p2) {
+
+    let {
+        result,
+        n
+    } = prepare(p1, p2);
     for (let i = 0; i < result.length; i++) {
         result[i] = (p1.coefficients[i] + p2.coefficients[i]) % n;
     }
@@ -31,20 +48,10 @@ function add(p1, p2) {
 exports.add = add;
 
 function sub(p1, p2) {
-    let n;
-    if (p1.mod !== p2.mod) {
-        throw "different modulo"
-    } else {
-        n = p1.mod;
-    }
-    let len_p1 = p1.coefficients.length;
-    let len_p2 = p2.coefficients.length;
-    result = new Array(Math.max(len_p1, len_p2)).fill(0);
-    if (len_p1 > len_p2) {
-        for (let x = 0; x < len_p1 - len_p2; x++) p2.coefficients.push(0);
-    } else {
-        for (let x = 0; x < len_p2 - len_p1; x++) p1.coefficients.push(0);
-    }
+    let {
+        result,
+        n
+    } = prepare(p1, p2);
     for (let i = 0; i < result.length; i++) {
         result[i] = (p1.coefficients[i] - p2.coefficients[i]) % n;
     }
@@ -53,12 +60,7 @@ function sub(p1, p2) {
 exports.sub = sub;
 
 function sub(p1, p2) {
-    let n;
-    if (p1.mod !== p2.mod) {
-        throw "different modulo"
-    } else {
-        n = p1.mod;
-    }
+    let n = get_mod(p1, p2);
     let len_p1 = p1.coefficients.length;
     let len_p2 = p2.coefficients.length;
     result = new Array(Math.max(len_p1, len_p2)).fill(0);
@@ -75,12 +77,7 @@ function sub(p1, p2) {
 exports.add = add;
 
 function multiply(p1, p2) {
-    let n;
-    if (p1.mod !== p2.mod) {
-        throw "different modulo"
-    } else {
-        n = p1.mod;
-    }
+    let n = get_mod(p1, p2);
     let f = p1.coefficients;
     let g = p2.coefficients;
     result = new Array(f.length + g.length - 1).fill(0);
@@ -95,6 +92,15 @@ function multiply(p1, p2) {
 }
 exports.multiply = multiply;
 
+function power(p1, pow) {
+    let result = p1;
+    for (let i = 1; i < pow; i++) {
+        result = multiply(result, p1);
+    }
+    return result;
+}
+exports.power = power;
+
 function divide(p1, p2) {
     let n;
     if (p1.mod !== p2.mod) {