Checksum for PPs No in Javascript

elgan

I am looking for a recommended source to help with writing javascript for a checksum of a PPS NO. I am an evening student & my only resourse are class notes, which are limited to say the least. I have to lodge this assignment shortly. I have tried the library & the recommended books have been swallowed up by the day students!!.
Any help would be appreciated.

elgan:(

kayos

Google is your friend!

http://en.wikipedia.org/wiki/Personal_Public_Service_Number

Check Character

The format of the PPS number is seven digits plus a check character. A second character may be used. If so it is always a 'W'.

The check character is calculated using a weighted addition of all the numbers and modulus calculation. It therefore checks for incorrectly entered digits and for digit transposition (digits in the wrong order will alter the sum due to weightings).

Calculation

In reverse order, each digit is multiplied by a weight, 2, 3, and so on until the first digit is multiplied by 8. Add up each result. Divide by 23 and the remainder (modulus 23) will indicate the character position on the alphabet.

Thus the PPS number 1234567 will be calculated as the sum of 7*2, 6*3, 5*4, 4*5, 3*6, 2*7 and 1*8. This 112 when divided by 23 leaves a remainder of 20. The twentieth letter of the English alphabet is 'T'. The correct PPS number is therefore 1234567T.

Go code

h57xiucj2z946q

It doesn't really say what you have to do if you get a remainder of 0. http://emhain.wit.ie/~p02csd22/Emhain/final/finalreport.html#achieved doesn't seem accurate. Not only have they used incorrect number in their example, these lads say I is the 10th letter of alphabet, while its the ninth. They include a trailing 0 as part of the number in the calculation even though 0 muliplied by anything is always 0. The trailing number is not part of the final result. Either way, if your following the Wikipedia explanation, here is a simple scrappy C source, you can follow along when implementing a javascript version...

#include <stdio.h>

void usage(char* exe) {
     printf("Usage: &#37;s <PPS No.>\ne.g. %s 7654321", exe, exe);
}

int main(int argc, char** argv) {
       unsigned short y, weight, sum, tmp;
       
       if ((argc < 2) || (strlen(argv[1]) != 7)) {
          usage(argv[0]);
	      exit(1);
       }             
       
       weight = 2; sum = 0;
       
       for ( y = 7 ; y > 0; y--) {
           if ( ((int)argv[1][y-1] < 48) || ((int)argv[1][y-1] > 57) ) {
              usage(argv[0]); exit(1);
           }              
           sum += ((int)argv[1][y-1]-48) * weight;
           weight++;
       }
       tmp = sum % 23;   
       printf("Input:\t%s\nPPS:\t%s%c\n",argv[1],argv[1],tmp+64);       
}

C:\>pps.exe 3984033
Input:  3984033
PPS:    3984033I

C:\>pps.exe 1234567
Input:  1234567
PPS:    1234567T

DublinDilbert

Well they are doing a modulo 23 division, so they are not using all the letters for the checksum, they are only using 23....

I would assume they are not using "o", "i" in case they get mixed up with "0" and "1"... i read the wiki earlier and "w" was used for "wife".... so maybe they just use the remaining 23 letters??

So you can't calculate the ASCII code of the letter by adding 64 to the remainder:-
tmp = sum % 23;
printf("Input:\t%s\nPPS:\t%s%c\n",argv[1],argv[1],tmp+64);


You'll need to use tmp to index down an array which contains the 23 valid check character values in order....

h57xiucj2z946q

dunno, need a more solid document on this.

fletch

Emma Tiny Software wrote: »

It doesn't really say what you have to do if you get a remainder of 0.

Yeh what do you do in the case of 0? Take for example the PPS Number 2495874. The formula will give an answer of 184, then modulus that by 23 will give 0.

Edit - just read kayos' comment above and see that it automatically defaults to 'W'.

dingding

Any ideas if it is possible to check the validity of a PPS no in excel?, say as an input to excel via a form.

seamus

The calculation to verify it is here:
http://en.wikipedia.org/wiki/Personal_Public_Service_Number#Calculation

You could write your own VBScript function in Excel to do a check on the number.

dingding

DublinDilbert wrote: »

Well they are doing a modulo 23 division, so they are not using all the letters for the checksum, they are only using 23....

I would assume they are not using "o", "i" in case they get mixed up with "0" and "1"... i read the wiki earlier and "w" was used for "wife".... so maybe they just use the remaining 23 letters??

So you can't calculate the ASCII code of the letter by adding 64 to the remainder:-
tmp = sum % 23;
printf("Input:\t%s\nPPS:\t%s%c\n",argv[1],argv[1],tmp+64);


You'll need to use tmp to index down an array which contains the 23 valid check character values in order....

My number used an o as the check digit, so they must use o as one of the letters.

cython

If you can understand PHP, then the Validate_IE class in PEAR has a pre-written method for this which is available open source. You can also establish how it handles a 0 remainder, etc. from it.