CRC

crc.js

/* 
    Cyclic redundancy check (CRC-4, CRC-8, CRC-16, CRC-32) 

    Common CRC implementation supporting wide range of configurations:
    http://reveng.sourceforge.net/crc-catalogue/all.htm
    
    NOTE: These common polynomials are likely suboptimal.
    In the future I should make a page of Koopman's best general purpose polynomials.

    http://github.com/bryc
*/

// :::::::::::::::: CRC-4/ITU ::::::::::::::::
var crc4 = function(data) {
    var POLY = 0xC, INIT = 0, XOROUT = 0;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ data[i];
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
    }
    return (crc ^ XOROUT) & 0xF;
};


// :::::::::::::::: CRC-4/ITU (lookup table) ::::::::::::::::
var crc4 = function(data) {
    var POLY = 0xC, INIT = 0, XOROUT = 0;
    for(var crc = 0, i = 0, table = []; i < 256; i++) {
        crc = i;
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
        table[i] = crc & 0xF;
    }
    return function(data) {
        for(var crc = INIT, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ crc & 0xFF] ^ crc >>> 8;
        }
        return (crc ^ XOROUT) & 0xF;
    }
}();


// :::::::::::::::: CRC-8/ITU ::::::::::::::::
var crc8 = function(data) {
    var POLY = 0x07, INIT = 0, XOROUT = 0x55;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ data[i];
        for(var j = 0; j < 8; j++) {
            crc = crc & 0x80 ? crc << 1 ^ POLY : crc << 1;
        }
    }
    return (crc ^ XOROUT) & 0xFF;
};


// :::::::::::::::: CRC-8/ITU (lookup table) ::::::::::::::::
var crc8 = function(data) {
    var POLY = 0x07, INIT = 0, XOROUT = 0x55;
    for(var crc = INIT, i = 0, table = []; i < 256; i++) {
        crc = i;
        for(var j = 0; j < 8; j++) {
            crc = crc & 0x80 ? crc << 1 ^ POLY : crc << 1;
        }
        table[i] = crc & 0xFF;
    }
    return function(data) {
        for(var crc = 0, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ crc & 0xFF] ^ crc << 8;
        }
        return (crc ^ XOROUT) & 0xFF;
    }
}();


// :::::::::::::::: CRC-16/CCITT ::::::::::::::::
var crc16 = function(data) {
    var POLY = 0x8408, INIT = 0, XOROUT = 0;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ data[i];
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
    }
    return (crc ^ XOROUT) & 0xFFFF;
};


// :::::::::::::::: CRC-16/CCITT (lookup table) ::::::::::::::::
var crc16 = function(data) {
    var POLY = 0x8408, INIT = 0, XOROUT = 0;
    for(var crc = INIT, i = 0, table = []; i < 256; i++) {
        crc = i;
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
        table[i] = crc & 0xFFFF;
    }
    return function(data) {
        for(var crc = 0, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ crc & 0xFF] ^ crc >>> 8;
        }
        return (crc ^ XOROUT) & 0xFFFF;
    }
}();


//:::::::::::::::: CRC-16/CCITT-FALSE ::::::::::::::::
var crc16b = function(data) {
    var POLY = 0x1021, INIT = 0xFFFF, XOROUT = 0;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ (data[i] << 8);
        for(var j = 0; j < 8; j++) {
            crc = crc & 0x8000 ? crc << 1 ^ POLY : crc << 1;
        }
    }
    return (crc ^ XOROUT) & 0xFFFF;
};


//:::::::::::::::: CRC-16/CCITT-FALSE (lookup table) ::::::::::::::::
var crc16b = function(data) {
    var POLY = 0x1021, INIT = 0xFFFF, XOROUT = 0;
    for(var crc = 0, i = 0, table = []; i < 256; i++) {
        crc = i << 8;
        for(var j = 0; j < 8; j++) {
            crc = crc & 0x8000 ? crc << 1 ^ POLY : crc << 1;
        }
        table[i] = crc & 0xFFFF;
    }
    return function(data) {
        for(var crc = INIT, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ (crc >>> 8) & 0xFF] ^ crc << 8;
        }
        return (crc ^ XOROUT) & 0xFFFF;
    }
}();


//:::::::::::::::: CRC-32 ::::::::::::::::
var crc32 = function(data) {
    var POLY = 0xEDB88320, INIT = -1, XOROUT = -1;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ (data[i]);
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
    }
    return (crc ^ XOROUT) >>> 0;
};


//:::::::::::::::: CRC-32 (lookup table) ::::::::::::::::
var crc32 = function(data) {
    var POLY = 0xEDB88320, INIT = -1, XOROUT = -1;
    for(var crc = 0, i = 0, table = []; i < 256; i++) {
        crc = i;
        for(var j = 0; j < 8; j++) {
            crc = crc & 1 ? crc >>> 1 ^ POLY : crc >>> 1;
        }
        table[i] = crc >>> 0;
    }
    return function(data) {
        for(var crc = INIT, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ crc & 0xFF] ^ crc >>> 8;
        }
        return (crc ^ XOROUT) >>> 0;
    }
}();


//:::::::::::::::: CRC-32/BZIP2 ::::::::::::::::
var crc32b = function(data) {
    var POLY = 0x04C11DB7, INIT = -1, XOROUT = -1;
    for(var crc = INIT, i = 0; i < data.length; i++) {
        crc = crc ^ (data[i] << 24);
        for(var j = 0; j < 8; j++) {
            crc = crc & 0x80000000 ? crc << 1 ^ POLY : crc << 1;
        }
    }
    return (crc ^ XOROUT) >>> 0;
};


//:::::::::::::::: CRC-32/BZIP2 (lookup table) ::::::::::::::::
var crc32b = function(data) {
    var POLY = 0x04C11DB7, INIT = -1, XOROUT = -1;
    for(var crc = 0, i = 0, table = []; i < 256; i++) {
        crc = i << 16;
        for(var j = 0; j < 16; j++) {
            crc = crc & 0x80000000 ? crc << 1 ^ POLY : crc << 1;
        }
        table[i] = crc >>> 0;
    }
    return function(data) {
        for(var crc = INIT, i = 0; i < data.length; i++) {
            crc = table[data[i] ^ (crc >>> 24) & 0xFF] ^ crc << 8;
        }
        return (crc ^ XOROUT) >>> 0;
    }
}();

zold.js

// ---- Important Links -------------------------------------------------------------------------------------
// http://reveng.sourceforge.net/crc-catalogue/all.htm
// https://archive.is/Yjh32#selection-375.0-375.9
// https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Polynomial_representations_of_cyclic_redundancy_checks
// http://crppit.epfl.ch/documentation/Hash_Function/WiKi/Cyclic_redundancy_check.htm
// http://www.zorc.breitbandkatze.de/crc.html
// https://users.ece.cmu.edu/~koopman/crc/crc4.html
// http://www.ross.net/crc/download/crc_v3.txt
// http://www.sunshine2k.de/articles/coding/crc/understanding_crc.html

// just some old crc32 code for posterity
var crc32 = function(data)
{
	for(var i=256, tbl=[], crc, j; i--; tbl[i]=crc>>>0){
		j=8;for(crc=i;j--;)crc=crc&1?crc>>>1^0xEDB88320:crc>>>1;
	}
	return function(str) {
		for(var i=0, crc=-1; i<data.length; ++i)
			crc=tbl[crc&255^data[i]]^crc>>>8;
		return crc^-1;
	}
}();

// Older implementation
    var crc32 = (function(data) {
        var table = [];
        for (var i = 256, crc; i--;) {
            crc = i;
            for (var j = 8; j--;) {
                if(crc & 1) {
                    crc = crc >>> 1 ^ 3988292384;
                }
                else {crc = crc >>> 1;}
            }
            table[i] = crc;
        }

        return function (data) {
            crc = -1;
            for (var i = 0; i < data.length; i++) {
                var ptr = crc & 255 ^ data[i];
                crc = crc >>> 8 ^ table[ptr];
            }
            crc = ((crc ^ -1) >>> 0).toString(16).toUpperCase();
            return ("00000000" + crc).slice(-8);
        }
    }());

I got a invalid value with this function(data = 'abc', valid result:20810, but got 52380):
var crc16b = function(data) {
var POLY = 0x1021, INIT = 0xFFFF, XOROUT = 0;
for(var crc = INIT, i = 0; i < data.length; i++) {
crc = crc ^ (data[i] << 8);
for(var j = 0; j < 8; j++) {
crc = crc & 0x8000 ? crc << 1 ^ POLY : crc << 1;
}
}
return (crc ^ XOROUT) & 0xFFFF;
};
Then I checked it, and changed data[i] to data.charCodeAt(i) , then got the valid result.

I got a invalid value with this function(data = 'abc', valid result:20810, but got 52380):
Then I checked it, and changed data[i] to data.charCodeAt(i) , then got the valid result.

Yes these functions take array as input, but you can swap with strings.
These are purely academic. For highly optimized implementations have a look here:
https://gist.github.com/bryc/79d1a62304773285317191f1ae5aa5b8