Comments on: Luhn Algorithm Validation in VBScript (ASP) http://www.nilpo.com/2009/02/windows-xp/luhn-algorithm-validation-in-vbscript-asp/ Ask the Windows Guru! Sat, 04 Feb 2012 12:10:33 +0000 http://wordpress.org/?v=2.3.1 By: Nilpo http://www.nilpo.com/2009/02/windows-xp/luhn-algorithm-validation-in-vbscript-asp/#comment-70916 Nilpo Fri, 11 Dec 2009 23:46:41 +0000 http://www.nilpo.com/2009/02/windows-xp/luhn-algorithm-validation-in-vbscript-asp/#comment-70916 The code processes from left to right, but it's done using logic. I've first determined the parity of each digit (it's even or odd position from the right). Since addition is cumulative, you can add from the left to the right or from the right to the left and come up with the same sum as long as you know the correct parity for processing each digit. I've used this approach to save on processing requirements as opposed to reversing the string or reading it directly from right to left (which requires reversing the string internally). The key is that finding a digit's parity achieves the same effect. The code processes from left to right, but it’s done using logic. I’ve first determined the parity of each digit (it’s even or odd position from the right).

Since addition is cumulative, you can add from the left to the right or from the right to the left and come up with the same sum as long as you know the correct parity for processing each digit.

I’ve used this approach to save on processing requirements as opposed to reversing the string or reading it directly from right to left (which requires reversing the string internally). The key is that finding a digit’s parity achieves the same effect.

]]> By: rush http://www.nilpo.com/2009/02/windows-xp/luhn-algorithm-validation-in-vbscript-asp/#comment-70908 rush Fri, 11 Dec 2009 21:44:07 +0000 http://www.nilpo.com/2009/02/windows-xp/luhn-algorithm-validation-in-vbscript-asp/#comment-70908 Your code does not match the text. The text says process each character from right to left, the code is processing then from left to right. Which is right? Your code does not match the text. The text says process each character from right to left, the code is processing then from left to right. Which is right?

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