#
# Modulus-10 in PostgreSQL 'plpgsql'.
#
# Tested on: Postgresql 7.x, 8.x
#
# (Modulus-10 is used for Credit Card number validation,
#  in Swedish social security numbers, bank account numbers,
#  organization numbers and more...)
#
# 
# Usage: SELECT modulo10( '<digits to calculate checksum for>' );
#
#                                              26th of December, 2005
#                                           http://netilium.org/~mad/
#                                 Martin Adolfsson <mad@netilium.org>
#

CREATE OR REPLACE FUNCTION _modulo10 ( INT4, INT4, TEXT ) RETURNS INT4 AS '
  DECLARE
    VAL INT4;
  BEGIN
    IF length($3) < 1 THEN
      RETURN (($2+(10-($2%10)))-$2)%10;
    ELSE
      SELECT INTO VAL (substring($3,1,1)::INT4)*($1+1);
      IF VAL > 9 THEN
        VAL := VAL - 9;
      END IF;
      RETURN _modulo10( ($1+1)%2, $2+VAL, substring( $3, 2 ) );
    END IF;
  END
' LANGUAGE 'plpgsql';

CREATE OR REPLACE FUNCTION modulo10 ( TEXT ) RETURNS INT4 AS 'SELECT _modulo10( 1, 0, $1 );' LANGUAGE 'sql';