How to resolve the algorithm Luhn test of credit card numbers step by step in the Forth programming language

Published on 12 May 2024 09:40 PM
#Forth

How to resolve the algorithm Luhn test of credit card numbers step by step in the Forth programming language

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Problem Statement

The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits. Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:

For example, if the trial number is 49927398716:

Write a function/method/procedure/subroutine that will validate a number with the Luhn test, and use it to validate the following numbers:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Luhn test of credit card numbers step by step in the Forth programming language

Source code in the forth programming language

: luhn ( addr len -- ? )
  0 >r over +             ( R: sum )
  begin  1- 2dup <=
  while                   \ odd
         dup c@ [char] 0 -
         r> + >r
         1- 2dup <=
  while                   \ even
         dup c@ [char] 0 -
         2* 10 /mod +     \ even digits doubled, split, and summed
         r> + >r
  repeat then
  2drop  r> 10 mod 0= ;

s" 49927398716"      luhn .   \ -1
s" 49927398717"      luhn .   \ 0
s" 1234567812345678" luhn .   \ 0
s" 1234567812345670" luhn .   \ -1

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