svdamani/crc32.js

## crc32.js
function CRC() {
    var table = new Array(256),     /// LookUp Table for CRC
        initial = 0xFFFFFFFF;       /// Initial CRC
    return {
        /// Reverse a polynomial
        reverse: function(poly) {
            var rev = 0;
            for(var i = 0; i < 32; i++) rev = rev << 1 | (poly >>> i) & 1;
            return rev;
        },
        /// Populate lookup table using the polynomial
        generate: function(poly) {
            for(var i = 0; i < 256; i++) {
                var n = i;
                for(var j = 8; j > 0; j--) {
                    n >>>= 1;
                    if((n & 1) == 1) n ^= poly;
                }
                table[i] = n;
            }
        },
        /// Compute the CRC of the given string using the polynomial
        compute: function(poly, data) {
            this.generate(poly);
            var crc = initial;
            for(var i = 0; i < data.length; i++)
                crc = (crc >>> 8) ^ table[data.charCodeAt(i) ^ (crc & 0x000000FF)];
            crc = ~crc;
            return crc < 0 ? initial + crc + 1 : crc;
        },
    };
};

## demo.html

<!DOCTYPE html>
<html>
<head>
    <script src="crc32.js"></script>
    <title>CRC - 32</title>
</head>
<body>
    <h2>CRC-32 Implementation in JavaScript</h2>
    <p>This is a simple crc generator using data and polynomial.</p>
    <p><b>Usage</b></p>
    <ul>
        <li>Enter data into the data field to get the 32 bit CRC</li>
        <li>To change the polynomial, just edit the polynomial field (either normal or reversed)</li>
        <li>To see the source code, <a href="crc32.js" target="_blank">click here</a></li>
    </ul>
    <form name="form1" action="javascript:void" autocomplete="off">
        <table>
            <tr>
                <td>Polynomial (normal)</td>
                <td>
                    <input type="text" name="polynomial" value="04C11DB7" onkeyup="onChangeNormal()" />
                    <button onclick="onResetClick()">Reset</button>
                </td>
            </tr>
            <tr>
                <td>Polynomial (reversed)</td>
                <td><input type="text" name="polyReversed" value="EDB88320" onkeyup="onChangeReversed()" /></td>
            </tr>
            <tr>
                <td>Input String</td>
                <td><textarea name="data" rows="5" cols="80" onkeyup="onChange()" autofocus></textarea></td>
            </tr>
            <tr>
                <td>Result (decimal)</td>
                <td><input type="text" name="decResult" readonly /></td>
            </tr>
            <tr>
                <td>Result (hexadecimal)</td>
                <td><input type="text" name="hexResult" readonly /></td>
            </tr>
        </table>
    </form>
    <script>
        String.prototype.repeat = function(times) {
            return (new Array(times + 1)).join(this);
        }
        Number.prototype.toHex = function(len) {
            len = len || 8;
            var num = this < 0 ? (0xFFFFFFFF + this + 1) : this;
            var hex = num.toString(16).toUpperCase();
            var pad = hex.length < len ? len - hex.length : 0;
            return "0".repeat(pad) + hex;
        }
        var form = document.form1,
            crc = new CRC();
        function onChangeNormal() {
            var polynomial = parseInt(form.polynomial.value, 16);
            form.polyReversed.value = polynomial ? crc.reverse(polynomial).toHex() : "";
            onChange();
        }
        function onChangeReversed() {
            var reversed = parseInt(form.polyReversed.value, 16);
            form.polynomial.value = reversed ? crc.reverse(reversed).toHex() : "";
            onChange();
        }
        function onChange() {
            var reversed = parseInt(form.polyReversed.value, 16);
            var data = form.data.value;
            var c = crc.compute(reversed, data);
            form.decResult.value = data ? c : "";
            form.hexResult.value = data ? c.toHex() : "";
        }
        function onResetClick() {
            form.polynomial.value = "04C11DB7";
            onChangeNormal();
            form.data.focus();
        }
    </script>
</body>
</html>
	function CRC() {
	var table = new Array(256), /// LookUp Table for CRC
	initial = 0xFFFFFFFF; /// Initial CRC
	return {
	/// Reverse a polynomial
	reverse: function(poly) {
	var rev = 0;
	for(var i = 0; i < 32; i++) rev = rev << 1 \| (poly >>> i) & 1;
	return rev;
	},
	/// Populate lookup table using the polynomial
	generate: function(poly) {
	for(var i = 0; i < 256; i++) {
	var n = i;
	for(var j = 8; j > 0; j--) {
	n >>>= 1;
	if((n & 1) == 1) n ^= poly;
	}
	table[i] = n;
	}
	},
	/// Compute the CRC of the given string using the polynomial
	compute: function(poly, data) {
	this.generate(poly);
	var crc = initial;
	for(var i = 0; i < data.length; i++)
	crc = (crc >>> 8) ^ table[data.charCodeAt(i) ^ (crc & 0x000000FF)];
	crc = ~crc;
	return crc < 0 ? initial + crc + 1 : crc;
	},
	};
	};

	<!DOCTYPE html>
	<html>
	<head>
	<script src="crc32.js"></script>
	<title>CRC - 32</title>
	</head>
	<body>
	<h2>CRC-32 Implementation in JavaScript</h2>
	<p>This is a simple crc generator using data and polynomial.</p>
	<p><b>Usage</b></p>
	<ul>
	<li>Enter data into the data field to get the 32 bit CRC</li>
	<li>To change the polynomial, just edit the polynomial field (either normal or reversed)</li>
	<li>To see the source code, <a href="crc32.js" target="_blank">click here</a></li>
	</ul>
	<form name="form1" action="javascript:void" autocomplete="off">
	<table>
	<tr>
	<td>Polynomial (normal)</td>
	<td>
	<input type="text" name="polynomial" value="04C11DB7" onkeyup="onChangeNormal()" />
	<button onclick="onResetClick()">Reset</button>
	</td>
	</tr>
	<tr>
	<td>Polynomial (reversed)</td>
	<td><input type="text" name="polyReversed" value="EDB88320" onkeyup="onChangeReversed()" /></td>
	</tr>
	<tr>
	<td>Input String</td>
	<td><textarea name="data" rows="5" cols="80" onkeyup="onChange()" autofocus></textarea></td>
	</tr>
	<tr>
	<td>Result (decimal)</td>
	<td><input type="text" name="decResult" readonly /></td>
	</tr>
	<tr>
	<td>Result (hexadecimal)</td>
	<td><input type="text" name="hexResult" readonly /></td>
	</tr>
	</table>
	</form>
	<script>
	String.prototype.repeat = function(times) {
	return (new Array(times + 1)).join(this);
	}
	Number.prototype.toHex = function(len) {
	len = len \|\| 8;
	var num = this < 0 ? (0xFFFFFFFF + this + 1) : this;
	var hex = num.toString(16).toUpperCase();
	var pad = hex.length < len ? len - hex.length : 0;
	return "0".repeat(pad) + hex;
	}
	var form = document.form1,
	crc = new CRC();
	function onChangeNormal() {
	var polynomial = parseInt(form.polynomial.value, 16);
	form.polyReversed.value = polynomial ? crc.reverse(polynomial).toHex() : "";
	onChange();
	}
	function onChangeReversed() {
	var reversed = parseInt(form.polyReversed.value, 16);
	form.polynomial.value = reversed ? crc.reverse(reversed).toHex() : "";
	onChange();
	}
	function onChange() {
	var reversed = parseInt(form.polyReversed.value, 16);
	var data = form.data.value;
	var c = crc.compute(reversed, data);
	form.decResult.value = data ? c : "";
	form.hexResult.value = data ? c.toHex() : "";
	}
	function onResetClick() {
	form.polynomial.value = "04C11DB7";
	onChangeNormal();
	form.data.focus();
	}
	</script>
	</body>
	</html>