ISO 7064

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ISO 7064 specifies a set of check character systems capable of protecting strings against errors which occur when people copy or key data.

Function StrMOD97

The function StrMOD97 can encode and verify number checksum with ISO 7064.

function StrMOD97(s: String): integer;
//Pre-condition: s can only contain digits, otherwise this function wil raise an exception.
const
  modu = 97;
var
  sx: String;
  isx, ic, p: Integer;
begin
   p := Length( s );
   while ( p > 9 ) do
     begin
       sx := Copy( s, 1, 9 );
       Delete( s, 1, 9 );
       isx := StrToInt( sx );
       ic := isx mod modu;
       s := IntToStr( ic ) + s;
       p := Length( s );
     end;
   isx := StrToInt( s );
   if isx >= modu
     then ic := isx mod modu
     else ic := isx;
  result := ic;
end;