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luhn-algorithm.js
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luhn-algorithm.js
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/*
* Luhn algorithm implementation in JavaScript
* Copyright (c) 2009 Nicholas C. Zakas
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
/**
* Uses Luhn algorithm to validate a numeric identifier.
* @param {String} identifier The identifier to validate.
* @return {Boolean} True if the identifier is valid, false if not.
*/
function isValidIdentifier(identifier) {
var sum = 0,
alt = false,
i = identifier.length-1,
num;
while (i >= 0){
//get the next digit
num = parseInt(identifier.charAt(i), 10);
//if it's not a valid number, abort
if (isNaN(num)){
return false;
}
//if it's an alternate number...
if (alt) {
num *= 2;
if (num > 9){
num = (num % 10) + 1;
}
}
//flip the alternate bit
alt = !alt;
//add to the rest of the sum
sum += num;
//go to next digit
i--;
}
//determine if it's valid
return (sum % 10 == 0);
}