The method based on locutus.io:
/* Source: locutus.io
* Fix: tutorialspots.com
*/
function unpack(format, data) {
var formatPointer = 0,
dataPointer = 0,
result = {},
instruction = '',
quantifier = '',
label = '',
currentData = '',
i = 0,
j = 0,
word = '',
fbits = 0,
ebits = 0,
dataByteLength = 0;
// Used by float decoding - by Joshua Bell
//http://cautionsingularityahead.blogspot.nl/2010/04/javascript-and-ieee754-redux.html
var fromIEEE754 = function(bytes, ebits, fbits) {
// Bytes to bits
var bits = [];
for (var i = bytes.length; i; i -= 1) {
var byte = bytes[i - 1];
for (var j = 8; j; j -= 1) {
bits.push(byte % 2 ? 1 : 0);
byte = byte >> 1;
}
}
bits.reverse();
var str = bits.join('');
// Unpack sign, exponent, fraction
var bias = (1 << (ebits - 1)) - 1;
var s = parseInt(str.substring(0, 1), 2) ? -1 : 1;
var e = parseInt(str.substring(1, 1 + ebits), 2);
var f = parseInt(str.substring(1 + ebits), 2);
// Produce number
if (e === (1 << ebits) - 1) {
return f !== 0 ? NaN : s * Infinity;
} else if (e > 0) {
return s * Math.pow(2, e - bias) * (1 + f / Math.pow(2, fbits));
} else if (f !== 0) {
return s * Math.pow(2, -(bias - 1)) * (f / Math.pow(2, fbits));
} else {
return s * 0;
}
}
while (formatPointer < format.length) {
instruction = format.charAt(formatPointer);
// Start reading 'quantifier'
quantifier = '';
formatPointer++;
while ((formatPointer < format.length) &&
(format.charAt(formatPointer).match(/[\d\*]/) !== null)) {
quantifier += format.charAt(formatPointer);
formatPointer++;
}
if (quantifier === '') {
quantifier = '1';
}
// Start reading label
label = '';
while ((formatPointer < format.length) &&
(format.charAt(formatPointer) !== '/')) {
label += format.charAt(formatPointer);
formatPointer++;
}
if (format.charAt(formatPointer) === '/') {
formatPointer++;
}
var countLabel = 0;
if (label == '') {
label = ++countLabel
}
// Process given instruction
switch (instruction) {
case 'a': // NUL-padded string
case 'A': // SPACE-padded string
if (quantifier === '*') {
quantifier = data.length - dataPointer;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier);
dataPointer += quantifier;
if (instruction === 'a') {
currentResult = currentData.replace(/\0+$/, '');
} else {
currentResult = currentData.replace(/ +$/, '');
}
result[label] = currentResult;
break;
case 'h': // Hex string, low nibble first
case 'H': // Hex string, high nibble first
if (quantifier === '*') {
quantifier = data.length - dataPointer;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier);
dataPointer += quantifier;
if (quantifier > currentData.length) {
throw new Error('Warning: unpack(): Type ' + instruction +
': not enough input, need ' + quantifier);
}
currentResult = '';
for (i = 0; i < currentData.length; i++) {
word = currentData.charCodeAt(i).toString(16);
if (instruction === 'h') {
word = word[1] + word[0];
}
currentResult += word;
}
result[label] = currentResult;
break;
case 'c': // signed char
case 'C': // unsigned c
if (quantifier === '*') {
quantifier = data.length - dataPointer;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier);
dataPointer += quantifier;
for (i = 0; i < currentData.length; i++) {
currentResult = currentData.charCodeAt(i);
if ((instruction === 'c') && (currentResult >= 128)) {
currentResult -= 256;
}
result[label + (quantifier > 1 ?
(i + 1) :
'')] = currentResult;
}
break;
case 'S': // unsigned short (always 16 bit, machine byte order)
case 's': // signed short (always 16 bit, machine byte order)
case 'v': // unsigned short (always 16 bit, little endian byte order)
if (quantifier === '*') {
quantifier = (data.length - dataPointer) / 2;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier * 2);
dataPointer += quantifier * 2;
for (i = 0; i < currentData.length; i += 2) {
// sum per word;
currentResult = ((currentData.charCodeAt(i + 1) & 0xFF) << 8) +
(currentData.charCodeAt(i) & 0xFF);
if ((instruction === 's') && (currentResult >= 32768)) {
currentResult -= 65536;
}
result[label + (quantifier > 1 ?
((i / 2) + 1) :
'')] = currentResult;
}
break;
case 'n': // unsigned short (always 16 bit, big endian byte order)
if (quantifier === '*') {
quantifier = (data.length - dataPointer) / 2;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier * 2);
dataPointer += quantifier * 2;
for (i = 0; i < currentData.length; i += 2) {
// sum per word;
currentResult = ((currentData.charCodeAt(i) & 0xFF) << 8) +
(currentData.charCodeAt(i + 1) & 0xFF);
result[label + (quantifier > 1 ?
((i / 2) + 1) :
'')] = currentResult;
}
break;
case 'i': // signed integer (machine dependent size and byte order)
case 'I': // unsigned integer (machine dependent size & byte order)
case 'l': // signed long (always 32 bit, machine byte order)
case 'L': // unsigned long (always 32 bit, machine byte order)
case 'V': // unsigned long (always 32 bit, little endian byte order)
if (quantifier === '*') {
quantifier = (data.length - dataPointer) / 4;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier * 4);
dataPointer += quantifier * 4;
for (i = 0; i < currentData.length; i += 4) {
currentResult =
((currentData.charCodeAt(i + 3) & 0xFF) << 24) +
((currentData.charCodeAt(i + 2) & 0xFF) << 16) +
((currentData.charCodeAt(i + 1) & 0xFF) << 8) +
((currentData.charCodeAt(i) & 0xFF));
result[label + (quantifier > 1 ?
((i / 4) + 1) :
'')] = currentResult;
}
break;
case 'N': // unsigned long (always 32 bit, little endian byte order)
if (quantifier === '*') {
quantifier = (data.length - dataPointer) / 4;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier * 4);
dataPointer += quantifier * 4;
for (i = 0; i < currentData.length; i += 4) {
currentResult =
((currentData.charCodeAt(i) & 0xFF) << 24) +
((currentData.charCodeAt(i + 1) & 0xFF) << 16) +
((currentData.charCodeAt(i + 2) & 0xFF) << 8) +
((currentData.charCodeAt(i + 3) & 0xFF));
result[label + (quantifier > 1 ?
((i / 4) + 1) :
'')] = currentResult;
}
break;
case 'f': //float
case 'd': //double
ebits = 8;
fbits = (instruction === 'f') ? 23 : 52;
dataByteLength = 4;
if (instruction === 'd') {
ebits = 11;
dataByteLength = 8;
}
if (quantifier === '*') {
quantifier = (data.length - dataPointer) / dataByteLength;
} else {
quantifier = parseInt(quantifier, 10);
}
currentData = data.substr(dataPointer, quantifier * dataByteLength);
dataPointer += quantifier * dataByteLength;
for (i = 0; i < currentData.length; i += dataByteLength) {
data = currentData.substr(i, dataByteLength);
bytes = [];
for (j = data.length - 1; j >= 0; --j) {
bytes.push(data.charCodeAt(j));
}
result[label + (quantifier > 1 ?
((i / 4) + 1) :
'')] = fromIEEE754(bytes, ebits, fbits);
}
break;
case 'x': // NUL byte
case 'X': // Back up one byte
case '@': // NUL byte
if (quantifier === '*') {
quantifier = data.length - dataPointer;
} else {
quantifier = parseInt(quantifier, 10);
}
if (quantifier > 0) {
if (instruction === 'X') {
dataPointer -= quantifier;
} else {
if (instruction === 'x') {
dataPointer += quantifier;
} else {
dataPointer = quantifier;
}
}
}
break;
default:
throw new Error('Warning: unpack() Type ' + instruction +
': unknown format code');
}
}
return result;
}
Example:
var str = "\xa0\x00\xa0\x00";
var result = unpack("Cchars/nint",str);
console.log(result)
Result:
Object {chars: 160, int: 160}
