Communication subsystem (simulation) using Hamming code
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// 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); | |
})(); | |
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can i get the html for this .js