Calculates the checksum of a given input of numbers using the Luhn Algorithm
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Calculate checksum using the Luhn Algorithm
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| function( | |
| a, // input number sequence as a string | |
| b, // placeholder | |
| c, // --||-- | |
| d){ // --||-- | |
| c=0; | |
| // traverse the input and multiply every other digit | |
| for(b in a) | |
| d=a[b],c+= | |
| b%2?+d // every other digit is just used straight away | |
| :d*2%10|d/5; // digits above 5 will result in double digits when | |
| // multiplied with 2 and should be added together | |
| // | |
| // 5*2 = 10 -> 1+0 = 1 | |
| // 6*2 = 12 -> 1+2 = 3 | |
| // 7*2 = 14 -> 1+4 = 5 | |
| // 8*2 = 16 -> 1+6 = 7 | |
| // 9*2 = 18 -> 1+8 = 9 | |
| // | |
| // digits below 5 are just multiplied by 2 | |
| // and this, is magic | |
| // multiply the sum by 9 and return the last digit | |
| return c*9%10 | |
| } |
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| function(a,b,c,d){c=0;for(b in a)d=a[b],c+=b%2?+d:d*2%10|d/5;return c*9%10} |
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| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2013 Johan Hillerström <https://github.com/hillerstorm> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
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| { | |
| "name": "luhnAlgorithm", | |
| "description": "Calculates a checksum using the Luhn algorithm.", | |
| "keywords": [ | |
| "luhn", | |
| "algorithm", | |
| "formula", | |
| "checksum" | |
| ] | |
| } |
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| <!DOCTYPE html> | |
| <title>Foo</title> | |
| <div>Expected value: <b>6</b></div> | |
| <div>Actual value: <b id="ret"></b></div> | |
| <script> | |
| var luhn = function(a,b,c,d){c=0;for(b in a)d=a[b],c+=b%2?+d:d*2%10|d/5;return c*9%10} | |
| document.getElementById('ret').innerHTML = luhn('811218987') | |
| </script> |
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A little boolean operator goes a long way :-)