From 68c43bfeb390b7f32082b0f32c9d61adae3c538e Mon Sep 17 00:00:00 2001
From: Kacper Kruczek <neronim66@gmail.com>
Date: Sun, 1 Jul 2018 15:14:54 +0200
Subject: [PATCH] 03 decode and encoded returns message and FCS

---
 03-rozwiazanie.js | 10 +++++--
 crc.js            | 74 ++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 65 insertions(+), 19 deletions(-)

diff --git a/03-rozwiazanie.js b/03-rozwiazanie.js
index 7532bb6..be5bc10 100644
--- a/03-rozwiazanie.js
+++ b/03-rozwiazanie.js
@@ -3,10 +3,16 @@ let message = process.argv[3];
 let flag = process.argv[2];
 switch (flag) {
     case '-e':
-        console.log(crc.encode(message));
+        console.log(crc.encode(message).encoded);
         break;
     case '-d':
-        console.log(crc.decode(message));
+        let fcs = JSON.parse(process.argv[4].replace(/'/g, '"'));
+
+        console.log(crc.decode(message, fcs));
+        break;
+    case '-t':
+
+
         break;
     default:
         throw "incorect flag"
diff --git a/crc.js b/crc.js
index d9ade17..d5f2180 100644
--- a/crc.js
+++ b/crc.js
@@ -1,7 +1,10 @@
 let Polynomial = require('./polynomial.js');
 
-const to_bytes_ascii = a => a.charCodeAt(0);
-const from_bytes_ascii = a => String.fromCharCode(a);
+let L = new Polynomial.Class(2, new Array(16).fill(1));
+let X = new Polynomial.Class(2, [0, 1]);
+let X16 = new Polynomial.Class(2, [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]); //jako ze można to od razu wymnożyć
+let G = new Polynomial.Class(2, [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1]); //jako ze można to od razu wymnożyć
+
 const to_bin = a => {
     var result = "";
     for (var i = 0; i < a.length; i++) {
@@ -13,28 +16,23 @@ const to_bin = a => {
 const to_ascii = a => {
     a = a.join('');
     a = parseInt(a, 2);
-    console.log(a)
     //nie znalazłem innego sposobu w js na osiągniecie tego efektu..
-    if (a < 126) //ponieważ wieksze liczby nie należą do typowego Ascii
-        return String.fromCharCode(a);
-    else {
-        return "0x" + a.toString(16);
-        //  return "\\x" + a.toString(16); //escape \ nie wiem czemu dobrze nie działą i i tak wypisuje \\
-    }
+    // if (a < 126) //ponieważ wieksze liczby nie należą do typowego Ascii
+    return String.fromCharCode(a);
+    // else {
+    //     return "0x" + a.toString(16);
+    //     //  return "\\x" + a.toString(16); //escape \ nie wiem czemu dobrze nie działą i i tak wypisuje \\
+    // }
 
 
 }
 
 const fcs = m => {
-    bits = m.map(to_bin); //message in binary
+    let bits = m.map(to_bin); //message in binary
     bits = bits.join('').split('').reverse(); //reverse binary decoded message
     let M = new Polynomial.Class(2, bits);
-    let L = new Polynomial.Class(2, new Array(16).fill(1));
-    let X = new Polynomial.Class(2, [0, 1]);
-    let X16 = Polynomial.power(X, 16);
-    let G = new Polynomial.Class(2, [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1]); //jako ze można to od razu wymnożyć
-
     let fcs = Polynomial.multiply(X16, M);
+
     fcs = Polynomial.add(fcs,
         Polynomial.multiply(
             Polynomial.power(X, m.length * 8),
@@ -47,6 +45,38 @@ const fcs = m => {
     return fcs.coefficients;
 }
 
+function mod8format(lst) {
+    while (lst.length % 8 != 0) {
+        lst.push(0);
+    }
+    return lst;
+}
+
+function check(m) {
+
+    let bits = m.map(to_bin); //message in binary
+    bits = bits.join('').split('').reverse(); //reverse binary decoded message
+
+    let fcs = Polynomial.power(X, bits.length);
+
+
+    let C = new Polynomial.Class(2, bits);
+    C = Polynomial.multiply(X16, C);
+    C.coefficients = mod8format(C.coefficients);
+    let S = Polynomial.add(
+        C,
+        Polynomial.multiply(
+            fcs,
+            L
+        )
+    )
+
+    S = Polynomial.divide(S, G)
+    if (S.coefficients.length === 0) {
+        return true;
+    } else
+        return false;
+}
 
 function encode(m) {
     m = m.split('');
@@ -65,13 +95,23 @@ function encode(m) {
     f2 = to_ascii(f2);
     m.push(f1);
     m.push(f2);
-    return m;
+    return {
+        encoded: m,
+        FCS: [f1, f2]
+
+    };
 
 }
 
 exports.encode = encode;
 
-function decode(m) {
+function decode(m, fcs) {
+    m = m.split('');
+    to_check = fcs;
+    for (let char in fcs) {
+        m.push(fcs[char]);
+    }
+    return check(m)
 
 }
 exports.decode = decode;
\ No newline at end of file