Base36 Conversion in PostgreSQL

CREATE OR REPLACE FUNCTION base36_encode(IN digits bigint, IN min_width int = 0)
  RETURNS varchar AS $$
        DECLARE
			chars char[];
			ret varchar;
			val bigint;
		BEGIN
		chars := ARRAY['0','1','2','3','4','5','6','7','8','9'
			,'A','B','C','D','E','F','G','H','I','J','K','L','M'
			,'N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
		val := digits;
		ret := '';
		IF val < 0 THEN
			val := val * -1;
		END IF;
		WHILE val != 0 LOOP
			ret := chars[(val % 36)+1] || ret;
			val := val / 36;
		END LOOP;
 
		IF min_width > 0 AND char_length(ret) < min_width THEN
			ret := lpad(ret, min_width, '0');
		END IF;
 
		RETURN ret;
 
END;
$$ LANGUAGE 'plpgsql' IMMUTABLE;

CREATE OR REPLACE FUNCTION base36_decode(IN base36 varchar)
  RETURNS bigint AS $$
        DECLARE
			a char[];
			ret bigint;
			i int;
			val int;
			chars varchar;
		BEGIN
		chars := '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
 
		FOR i IN REVERSE char_length(base36)..1 LOOP
			a := a || substring(upper(base36) FROM i FOR 1)::char;
		END LOOP;
		i := 0;
		ret := 0;
		WHILE i < (array_length(a,1)) LOOP		
			val := position(a[i+1] IN chars)-1;
			ret := ret + (val * (36 ^ i));
			i := i + 1;
		END LOOP;
 
		RETURN ret;
 
END;
$$ LANGUAGE 'plpgsql' IMMUTABLE;