Calculate parity bit for a string representation of a binary number, i.e 0101011101

get_facility_code_wiegan_length_from_format_name.js

var FACILITY_CODE = /(\d+)$/;
var WIEGAND_LENGTH = /^Wiegand (\d+)/i;

function getFacilityCode(format=''){
    let match = format.match(FACILITY_CODE);
    if(!match) return undefined;
    let code = match[1];
    return parseInt(code);
}

function getWiegandLength(format=''){
    let match = format.match(WIEGAND_LENGTH);
    if(!match) return undefined;
    let code = match[1];
    return parseInt(code);
}

console.assert(getFacilityCode('Wiegand 26-bit facility code 203') === 203);
console.assert(getWiegandLength('Wiegand 26-bit facility code 203') == 26);

console.assert(getFacilityCode('Wiegand 26 bit facility code 100') === 100);
console.assert(getWiegandLength('Wiegand 26 bit facility code 100') === 26);

console.assert(getFacilityCode('Wiegand 37 bit Facility Code 120') === 120);
console.assert(getWiegandLength('Wiegand 37 bit Facility Code 120') === 37);

console.assert(getFacilityCode('Wiegand 39 bit Bluetooth Facility Code 3') === 3);
console.assert(getWiegandLength('Wiegand 39 bit Bluetooth Facility Code 3') === 39);

parityBit.js

/**
 * Calculate parity bit for a binary sequence.
 * Given a string representing a binary number, 
 * this will calculate the even or odd parity bit.
 *
 * In the case of **even** parity, for a given set of 
 * bits, the occurrences of bits whose value is 1 
 * is counted. If that count is odd, the parity bit 
 * value is set to 1, making the total count of 
 * occurrences of 1's in the whole set 
 * (including the parity bit) an even number. 
 * If the count of 1's in a given set of bits is 
 * already even, the parity bit's value is 0.
 *
 * In the case of odd parity, the coding is 
 * reversed. For a given set of bits, if the count
 * of bits with a value of 1 is even, the parity 
 * bit value is set to 1 making the total count of
 * 1's in the whole set (including the parity bit) 
 * an odd number. 
 * If the count of bits with a value of 1 is odd, 
 * the count is already odd so the parity bit's 
 * value is 0.
 *
 * https://en.wikipedia.org/wiki/Parity_bit
 * https://www.hidglobal.com/sites/default/files/hid-understanding_card_data_formats-wp-en.pdf
 * http://www.ccdesignworks.com/wiegand_calc.htm
 * 
 * int    bin    1count    even |P      odd |P
 *  0   0000000    0      0000000|0    0000000|1
 *  81  1010001    3      1010001|1    1010001|0
 * 105  1101001    4      1101001|0    1101001|1
 * 127  1111111    7      1111111|1    1111111|0
 * 
 * @param  {String} bin          Binary number
 * @param  {String} [parity='e'] e:Even o:Odd  
 * @return {String}              
 */
function parityBit(bin='', parity = 'e'){
    function bitCount(bin){
        return (bin.match(/1/g) || []).length;
    }
    
    let isEven = bitCount(bin) % 2 === 0;
    if(parity.match(/^e$|^even$/i)) return isEven ? '0' : '1';
    return isEven ? '1' : '0';
}



console.assert(parityBit('0000000', 'e') === '0', 'Parity bit must be 0');
console.assert(parityBit('0000000', 'o') === '1', 'Parity bit must be 1');

console.assert(parityBit('1010001', 'e') === '1', 'Parity bit must be 1');
console.assert(parityBit('1010001', 'o') === '0', 'Parity bit must be 0');

console.assert(parityBit('1101001', 'e') === '0', 'Parity bit must be 0');
console.assert(parityBit('1101001', 'o') === '1', 'Parity bit must be 1');

console.assert(parityBit('1111111', 'e') === '1', 'Parity bit must be 1');
console.assert(parityBit('1111111', 'o') === '0', 'Parity bit must be 0');