Optimizations anyone?

Hi all ~ I just wrote the function below to validate Canadian Social Insurance numbers (SIN) and it strikes me as, well, rather awkward. SINs are 9 digits wide and the rightmost digit is the check digit. Any Rebolish ideas anyone? TIA Kai valid-sin: function [ sin [string!] ] [ digits8 ] [ if any [ 9 <> length? trim sin none = to-integer sin ] [ return false ] ; from left to right all even positions evens: copy "" sin: skip sin 1 forskip sin 2 [ evens: append evens form ( 2 * to-integer to-string first sin )] ; evens-sum: 0 foreach digit evens [ evens-sum: evens-sum + ( to-integer to-string digit )] ; ; from left to right all odd positions odds-sum: 0 digits8: copy/part head sin 8 forskip digits8 2 [ odds-sum: odds-sum + ( to-integer to-string first digits8 )] ; total-sum: evens-sum + odds-sum next-ten: 10 * (1 + to-integer to-string first to-string total-sum ) check-digit: next-ten - total-sum ; sin: head sin check-digit = ( to-integer to-string sin/9 ) ] ; 2 valid SINs valid-sin "130692544" valid-sin "193456787"

Hi Kai, KP> I just wrote the function below to validate Canadian Social InsuranceKP> numbers (SIN) and it strikes me as, well, rather awkward. Looks like SINs use the Luhn algorithm to calc the check digit. luhn?: func [ card-num [string!] /local cksum flag val ] [ cksum: 0 card-num: trim/all copy card-num flag: even? length? card-num foreach digit card-num [ val: to integer! form digit if flag [ val: val * 2 if val > 9 [val: val - 9] ; - alt - ;val: pick [0 2 4 6 8 1 3 5 7 9] val + 1 ] cksum: cksum + val flag: not flag ] ;print cksum 0 = remainder cksum 10 ] -- Gregg

You should add your implementation of Luhn validation script to Wikipedia... http://en.wikipedia.org/wiki/Luhn_algorithm

Thanks, Gregg ~ exactly what I was hoping for! Kai On Wed, 6 Feb 2008 14:25:36 -0700, Gregg Irwin wrote: