IMEI checksum help

[fddizon]

hi to all,

i have a code from visual basic that i would like to convert to xbasic but i dont know how to. here is the code...

Function Checksum(IMEI)
  On Error Resume Next
  Table = Array(Array(0, 8, 6, 4, 2, 9, 7, 5, 3, 1), Array(0, 9, 8, 7, 6, 5, 4, 3, 2, 1))
  Position = 1
  For I = 1 To 14
  Checksum = Checksum + Table(Position)(Mid(IMEI, I, 1))

  If Position = 1 Then
     Position = 0
  Else
     Position = 1
  End If
  Next I
 
  Do While Checksum >= 10
  Checksum = Checksum - 10
  Loop

End Function

if there's anyone on the board that has a working IMEI checksum function, please help.

or someone who can convert the above vb code to xbasic

thanks a lot in advance

[G Gabriel]

Re: IMEI checksum help

Here is a sample function:

FUNCTION IMEI_Valid AS L (IMEI AS C )
ln=len(IMEI)
dim x as c=""
for i=1 to ln
x=x+substr(IMEI,i,1)+crlf()
next
x=crlf_to_comma(x)
x=*reverse_words(x,",")
dim k as n
dim cksm as n
for i=1 to ln
	k=val(word(x,i,","))
	cksm=cksm+if(mod(i,2)=0,k*2,k)
	next
IMEI_Valid=if(mod(cksm,10)=0,.t.,.f.)
END FUNCTION

?imei_valid("1234567890")
= .T.

[fddizon]

Re: IMEI checksum help

hi gabriel,

thanks for the sample...
i tried testing the sample with a valid imei, it gave a false result.

here is the detailed instructions on how to compute the 15th digit of the imei that i took from a forum i searched on the net.

The last number of the IMEI is called the Check Digit and is defined using a formula 
called "Luhn formula", thus sometimes the last digit is called the Luhn Check Digit and 
does not necessarily always set to 0.

This check digit is computed in three steps as follows:

Given:
14 most significant digits of the IMEISV without the SVN which are the 
6-digit TAC, 
2-digit FAC, 
6-digit SNR and are labelled as follows:

TAC = D14 D13 ... D9 (with D9 the least significant digit of TAC);
FAC = D8 D7 (with D7 the least significant digit of FAC); and
SNR = D6 D5 ... D1 (with D1 the least significant digit of SNR).

Example IMEI: [ 490154 20 323751 ? ] (ignore the last digit)

FAC: 490154

D14:4
D13:9
D12:0
D11:1
D10:5
D09:4
----------
TAC: 20

D08:2
D07:0
----------
SNR: 323751

D06:3
D05:2
D04:3
D03:7
D02:5
D01:1

CHK: ?

Computation of CHK from the IMEI proceeds as follows:
================================================== ====

Step 1: 
Double the values of the odd labelled digits D1, D3, D5 ... D13 of the IMEI.
490154 20 323751
------------------
.D14:4=4
*D13:9x2=18
.D12:0=0
*D11:1x2=2
.D10:5=5
*D09:4x2=8
.D08:2=2
*D07:0x2=0
.D06:3=3
*D05:2x2=4
.D04:3=3
*D03:7x2=14
.D02:5=5
*D01:1x2=2
//================================================== ============================
Step 2: Add together the individual digits of all the seven numbers obtained in 
Step 1,

1+8 + 2 + 8 + 0 + 4 + 1+4 + 2 = 30

and then add this sum to the sum of all the even labelled digits 
D2, D4, D6 ... D14 of the IMEI.
4 + 0 + 5 + 2 + 3 + 3 + 5 = 22

The result is:
30 + 22 = 52
or
4 + 1+8 + 0 + 2 + 5 + 8 + 2 + 0 + 3 + 4 + 3 + 1+4 + 5 + 2 = 52
//================================================== ===========================
Step 3: If the number obtained in Step 2 ends in 0, then set CHK to be 0. 
If the number obtained in Step 2 does not end in 0, then set CHK to be 
that number subtracted from the next higher number which does end in 0.

Since 52 ends in "2", CHK can't be set to "0". The next higher number that does 
end in "0" after 52 is 60, so we set:

CHK = 60 - 52 = 8

So the IMEI number is: 490154203237518 and it ends in 8.

P.S. The IMEI number sampled above is fictios and does not reflect nor intended for
an existing IMEI number.

here is a valid imei: 352526032177436

can you try to convert this again in xbasic?
i will try also to convert this based on your first function.

tia

[G Gabriel]

Re: IMEI checksum help

I meant this only as a sample for you to modify according to whichever formula is used.
When I get a little more time, I will apply our formula.

[fddizon]

Re: IMEI checksum help

hi to all,

gabriel, thanks for the sample code.

i came up with this function based on posted pseudo code.

'Date Created: 01-Aug-2010 01:09:31 PM
'Last Updated: 16-Aug-2010 01:37:53 PM
'Created By  : fdd
'Updated By  : fdd

FUNCTION IMEI_Valid AS L (IMEI AS C)

	dim ln as n = 0
	dim d1 as n = 0
	dim d2 as n = 0
	dim d3 as n = 0
	dim d4 as n = 0
	dim d5 as n = 0
	dim d6 as n = 0
	dim d7 as n = 0
	dim d8 as n = 0
	dim d9 as n = 0
	dim d10 as n = 0
	dim d11 as n = 0
	dim d12 as n = 0
	dim d13 as n = 0
	dim d14 as n = 0
	dim d15 as n = val(substr(IMEI,15,1))
	dim x as c=""	
	
	ln = len(imei)-1
	for i=1 to ln
	x=substr(IMEI,i,1)

	if i = 1 then
	    d1 = val(x)
	elseif i = 2 then
		d2 = val(x)
	elseif i = 3 then
		d3 = val(x)
	elseif i = 4 then
		d4 = val(x)
	elseif i = 5 then
		d5 = val(x)
	elseif i = 6 then
		d6 = val(x)
	elseif i = 7 then
		d7 = val(x)
	elseif i = 8 then
		d8 = val(x)
	elseif i = 9 then
		d9 = val(x)
	elseif i = 10 then
		d10 = val(x)
	elseif i = 11 then
		d11 = val(x)
	elseif i = 12 then
		d12 = val(x)
	elseif i = 13 then
		d13 = val(x)
	elseif i = 14 then
		d14 = val(x)
	end if
	
	next
	
	d1 = d1 * 2
	d3 = d3 * 2
	d5 = d5 * 2
	d7 = d7 * 2
	d9 = d9 * 2
	d11 = d11 * 2
	d13 = d13 * 2

	dim vFinal as n

	if len(alltrim(str(d1))) = 2 then	
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d1))) then
			dtmp = alltrim(str(d1))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d1 = tmpfinal
		end if 
	elseif len(alltrim(str(d3))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d3))) then
			dtmp = alltrim(str(d3))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d3 = tmpfinal
		end if 
	elseif len(alltrim(str(d5))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d5))) then
			dtmp = alltrim(str(d5))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d5 = tmpfinal
		end if 
	elseif len(alltrim(str(d7))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d7))) then
			dtmp = alltrim(str(d7))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d7 = tmpfinal
		end if 
	elseif len(alltrim(str(d9))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d9))) then
			dtmp = alltrim(str(d9))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d9 = tmpfinal
		end if 
	elseif len(alltrim(str(d11))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d11))) then
			dtmp = alltrim(str(d11))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d11 = tmpfinal
		end if 
	elseif len(alltrim(str(d13))) = 2 then
	    dim dtmp as c = ""
		dim dtmp1 as c = ""
		dim dtmp2 as c = ""
		dim fin1 as n
		dim fin2 as n
		dim tmpfinal as n		
		if len(alltrim(str(d13))) then
			dtmp = alltrim(str(d13))
			dtmp1 = substr(dtmp,1,1)
			dtmp2 = substr(dtmp,2,1)
			tmpfinal = val(dtmp1) + val(dtmp2)
			d13 = tmpfinal
		end if 
	
	end if	
	
	vFinal = d1 + d3 + d5 + d7 + d9 + d11 + d13 + d2 + d4 + d6 + d8 + d10 + d12 + d14
	dim rem as n
	rem = mod(vFinal, 10)
	
    if  rem = 0 then
        if d15 = 0 then
			msgbox(vSystem_name, "IMEI is valid")
		end if	
	else
		dim hul as n
		dim notzero as n
		hul = 10*int(vFinal/10)
		notzero = (hul + 10) - vFinal
		if	d15 = notzero then
			msgbox(vSystem_name, "IMEI is valid")
		else
			cancel()
			msgbox(vSystem_Name, "Invalid IMEI. Please enter the correct IMEI to continue.",UI_ATTENTION_SYMBOL+UI_OK)						    
		end if
    end if

END FUNCTION

can someone help assess if the function complied the pseudo code?
I'm not getting the correct last digit. it seems like the pseudo code is not correct. :( (i took that from a vb forum)

is there anyone knows how to calculate the cellphone's imei?

thanks in advance

[Tim Kiebert]

Re: IMEI checksum help

I think part of your problem is that in your first step you are doubling the digits starting from the left instead of the right. (according to the article in wikipedia) That is, d1 should be substr(IMEI,14,1) So in your code you should be doubling d2,d4,d6,d8,d10,d12,d14.

This what I came up with. I think it works. I left the test message boxes in so you can see what is happening.

FUNCTION IMEI_Valid AS L (IMEI AS C)
'Description: This function checks a 15 digit IMEI code for a correct check digit.
    'There is also a 16 digit code which is a IMEISV. It does not have a check digit.
    IMEI_Valid = .f.
    IMEI = remspecial(IMEI)
    If len(IMEI) <> 15 then
        exit function
    end if
    
    
    dim expression as C = ""
    dim exp_calc as C = ""
    dim exp_len as N
    dim exp_sum as N
    dim chkdigitn as N
    'Create a string of digits by doubling in value every second original digit.
    expression =    substr(IMEI,1,1)+ (val(substr(IMEI,2,1))*2) + \
                    substr(IMEI,3,1)+ (val(substr(IMEI,4,1))*2) + \
                    substr(IMEI,5,1)+ (val(substr(IMEI,6,1))*2) + \
                    substr(IMEI,7,1)+ (val(substr(IMEI,8,1))*2) + \
                    substr(IMEI,9,1)+ (val(substr(IMEI,10,1))*2) + \
                    substr(IMEI,11,1)+ (val(substr(IMEI,12,1))*2) + \
                    substr(IMEI,13,1)+ (val(substr(IMEI,14,1))*2)
    msgbox("After doubling every other digit",expression) 'For testing
    
    'create an expression in character format inserting a '+' between each digit in the result from above
    exp_len = len(expression)
    For dgt = 1 to exp_len
        exp_calc = exp_calc + substr(expression,dgt,1)
        If dgt < exp_len then      'If dgt is not less than exp_len then it is the last digit so don't add a '+'
            exp_calc = exp_calc + "+"
        end if
    Next
    msgbox("expression to sum up resulting digits",exp_calc)  'For testing
    
    'evaluate the expression
    exp_sum = eval(exp_calc)
    
    msgbox(""+exp_sum)   'For testing
    
    chkdigitn = 10 - mod(exp_sum,10)
    if chkdigitn = 10 then
        chkdigitn = 0
    end if
    
    If chkdigitn = val(substr(IMEI,15,1)) then
        IMEI_Valid = .t.
    end if
    msgbox("Final","This IMEI is "+IMEI_Valid)   'For testing
    
    
END FUNCTION

[fddizon]

Re: IMEI checksum help

tim,

big thanks....

i owe you another beer... :)

thanks!

[Tim Kiebert]

Re: IMEI checksum help

Your welcome.

Let us know if it behaves consistently.

[pboomwork]

Re: IMEI checksum help

I am posting this information in case someone at some point needs to check Canadian health card numbers.

In Canada a MOD 10 Check Digit is added to the Health Card Number used by several provinces. The Health Card Number (HCN) is a provincially issued number and ID card that is used to track health care services insured or paid for by the provincial government. It is the primary ID for many health care information systems, one of which I find myself working with now.

With a few modifications the code provided by Tim Kiebert was modified to work with Ontario and Nova Scotia HCN. It may work with other provinces but they where not tested.

Thanks Tim for the original code it is much more efficient then anything I could come up with. I was envisioning loops with lots of branching.

FUNCTION HCN_Valid AS L (HCN AS C )
	'Description: This function checks a 10 digit Health Card Numer for a correct check digit.
    HCN_Valid = .f.
    HCN = remspecial(HCN)
    If len(HCN) <> 10 then
        exit function
    end if
    
    dim expression as C = ""
    dim exp_calc as C = ""
    dim exp_len as N
    dim exp_sum as N
    dim chkdigitn as N
    'Create a string of digits by doubling in value every second original digit.
    expression = 	(val(substr(HCN,1,1))*2) + substr(HCN,2,1) + \
    				(val(substr(HCN,3,1))*2) + substr(HCN,4,1) + \
					(val(substr(HCN,5,1))*2) + substr(HCN,6,1) + \
					(val(substr(HCN,7,1))*2) + substr(HCN,8,1) + \
					(val(substr(HCN,9,1))*2)

    '!Debug stuff
    'msgbox("After doubling every other digit: ",expression)
    
    'create an expression in character format inserting a '+' between each digit in the result from above
    exp_len = len(expression)
    For dgt = 1 to exp_len
        exp_calc = exp_calc + substr(expression,dgt,1)
        If dgt < exp_len then      'If dgt is not less than exp_len then it is the last digit so don't add a '+'
            exp_calc = exp_calc + "+"
        end if
    Next
    '!Debug Stuff
    'msgbox("expression to sum up resulting digits: ",exp_calc)
    
    'evaluate the expression
    exp_sum = eval(exp_calc)
    
    '!Debug stuff
    'msgbox("Sum of numbers: "+exp_sum)
    
    chkdigitn = 10 - mod(exp_sum,10)
    if chkdigitn = 10 then
        chkdigitn = 0
    end if
    
    If chkdigitn = val(substr(HCN,10,1)) then
        HCN_Valid = .t.
    end if
    
    '!Debug Stuff
    'msgbox("Final","This HCN is "+HCN_Valid)
    
END FUNCTION