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> |
Doesn't give the same output :o
It does for the example (811218987) but not for e.g. 870810563.
The checksum for the first example should be 6 and for the other one it should be 3
I believe this is due to operator precedence.
function(a,b,c,d){c=0;for(b in a)d=a[b],c+=b&1?d*2%10+d>4:+d;return c*9%10}
If that also failed, then the modulo has higher precedence than the multiplication and the latter would require brackets.
It was operator precedence, but on the comparison rather than the calculation.
function(a,b,c,d){c=0;for(b in a)d=a[b],c+=b%2?+d:d*2%10+(d>4);return c*9%10}
I'll try to find a smaller version without the brackets.
A little boolean operator goes a long way :-)
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}
:D
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