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@tjwudi
Last active February 8, 2016 08:01
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Communication subsystem (simulation) using Hamming code
// needs async library support
var
async = require('async');
(function lifeCycle(){
var
workflow = {
body : [],
end : function() {},
util : {},
conf : {}
},
msg = null; // message the user want to send
workflow.conf = {
pError : 100 // just let the error occur
}
workflow.util.genError = function(){
if (Math.floor(Math.random() * 100) < workflow.conf.pError) {
return Math.floor(Math.random() * (msg.length - 1));
}
else {
return null;
}
}
// Check if num is power of 2
workflow.util.is2pow = function(num){
return !!((num & (num - 1)) == 0);
}
workflow.body.push(function readMessage(next){
process.stdin.resume();
console.log('Enter a short binary message (one line):');
process.stdin.on('data', function(chunk){
// Here I use Buffer class in Node.js instead of string
msg = chunk;
process.stdin.pause();
next();
});
});
workflow.body.push(function addParityCodes(next){
var tmp = new Buffer(1000);
tmp.fill(0x0a);
var
posInMsg = 0,
tmpLen = 0;
for (var i = 0; i < 1000; i ++) {
// The real position for code at index i is (i + 1)
// we now check if i + 1 is power of 2
if (workflow.util.is2pow(i + 1)) {
tmp[i] = 0xFF; // 0xFF is a placeholder for parity code
}
else {
tmp[i] = msg[posInMsg];
posInMsg ++;
if (posInMsg === msg.length - 1) {
// no more code
tmpLen = i + 2;
break;
}
}
}
// determine parity code
var step = 1;
for (var i = 0; i < tmpLen - 1; i ++) {
if (tmp[i] != 0xFF) {
continue;
}
var
result = 0,
j = i;
while (j < tmpLen - 1) {
for (var k = 0; k < step && j + k < tmpLen - 1; k ++) {
if (tmp[j + k] > 49) {
// the parity code itself
continue;
}
result ^= (tmp[j + k] - 48);
}
j += (2 * step);
}
tmp[i] = result + 48;
step *= 2;
}
// assign updated message
var newMsg = new Buffer(tmpLen);
tmp.copy(newMsg, 0, 0, tmpLen);
msg = newMsg;
console.log('The message with parity codes:\n' + msg.toString());
next();
});
// Generate error randomly
// the probability of error occurence is determined by conf.pError
workflow.body.push(function makeError(next){
var errorIndex = workflow.util.genError();
if (errorIndex) {
msg[errorIndex] = msg[errorIndex] === 49 ? 48 : 49;
console.log('Error occurred at position: ' + (errorIndex+1));
}
console.log('Received message:\n' + msg);
next();
});
// Check for the single bit error
// if the error occurred, then correct it!
workflow.body.push(function errorProcess(next){
var step = 1,
errorIndex = 0;
for (var i = 0; i < msg.length - 1; i ++) {
if (! workflow.util.is2pow(i + 1)) {
continue;
}
var
result = 0,
j = i;
while (j < msg.length - 1) {
for (var k = 0; k < step && j + k < msg.length - 1; k ++) {
result ^= (msg[j + k] - 48);
}
j += (2 * step);
}
if (result != 0) {
// error spotted
errorIndex += step;
}
step *= 2;
}
if (errorIndex > 0) {
console.log('Error founded at index:', errorIndex);
msg[errorIndex - 1] = msg[errorIndex - 1] == 48 ? 49 : 48;
}
console.log('The message is:\n' + msg.toString());
next();
});
workflow.end = function(err){
if (err) {
throw err;
}
else {
console.log('--------------------------------------');
lifeCycle();
}
}
async.series(workflow.body, workflow.end);
})();
@Tallbert
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Tallbert commented Feb 8, 2016

can i get the html for this .js

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