SQL modulus 10 LUHN check and calculation

modulus10.sql

------------------------------------------------------- 
-- Implements LUHN modulus 10 for credit card checksum
-- Niels Liisberg 
------------------------------------------------------- 
create or replace function qusrsys.modulus10 (inString varchar(32))                                       
    returns int   
    language sql                                                                           
    reads sql data                                                                          
    returns null on null input                                                               
    no external action                                                                      
    deterministic 
    set option dbgview = *source , output=*print                                                                          
            
begin atomic                                                
    declare len      int default 0;                                    
    declare checksum int default 0;  
    declare d        int default 0;
    declare parity   int default 0;
                                    
    set len = length(inString);
    set parity = mod ( len , 2); 
    
    while len > 0 do
        set d  = int(substring(inString , len ,1));
        if mod (len , 2) <> parity  then
            set d = d *2;
            if  d > 9 then
                set d = d -9;
            end if;
        end if;
        set checksum = checksum + d;
        set len = len - 1;
    end while;
    return mod ( checksum , 10 ) ;
 end;
 
create or replace function qusrsys.modulus10calculate (inString varchar(32))                                       
    returns int   
    language sql                                                                           
    reads sql data                                                                          
    returns null on null input                                                               
    no external action                                                                      
    deterministic 
    set option dbgview = *source , output=*print                                                                          
            
begin atomic                                                
    declare len      int default 0;                                    
    declare checksum int default 0;  
    declare d        int default 0;
    declare parity   int default 0;
              
    set checksum = qusrsys.modulus10( inString concat '0');
    if checksum = 0 then 
        return 0;
    else
        return 10 - checksum;
    end if;
end;
 
create or replace function qusrsys.modulus10validate (inString varchar(32))                                       
    returns int   
    language sql                                                                           
    reads sql data                                                                          
    returns null on null input                                                               
    no external action                                                                      
    deterministic 
    set option dbgview = *source , output=*print                                                                          
            
begin atomic                                                
    declare len      int default 0;                                    
    declare checksum int default 0;  
    declare d        int default 0;
    declare parity   int default 0;
              
    set checksum = qusrsys.modulus10( inString);
    if checksum = 0 then 
        return 1;
    else
        return 0;
    end if;
 end;
 
 -- This returns 0 
 values (
   qusrsys.modulus10('8527530000345267')
 );
 
 -- This returns 7 
 values (
   qusrsys.modulus10calculate('852753000034526')
 );
 
 -- This returns 1
 values (
   qusrsys.modulus10validate('8527530000345267')
 )