Re: Referring to function parameter in function

[Thom Brown <thom@xxxxxxxxx>]

On 18 September 2010 00:14, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
> Thom Brown <thom@xxxxxxxxx> writes:
>> ERROR:  invalid input syntax for integer: "bitlength"
>> LINE 1: SELECT GET_BIT(from_value::bit(bitlength), tap.value-1)
>>                                    ^
>
>> I want to use the parameter called "bitlength" as the length of a bit
>> when casting a value.
>
> Hm, you can't ... that's not a valid place for a parameter.  You'd have
> to EXECUTE a built-up string.

Ah, thanks Tom.  Although it's now treating the actual query text as a
value by the look of it:

CREATE OR REPLACE FUNCTION get_lsfr(
	bitlength INT,
	taps INT[],
	from_value INT
) RETURNS INT AS $$
DECLARE
	last_tap_value BIT;
	tap RECORD;
	new_value INT;
BEGIN	
	IF (SELECT MAX(x) FROM unnest(taps) AS x) > bitlength THEN
		RAISE EXCEPTION 'LSFR tap exceeds range of value.';
	END IF;

	FOR tap IN SELECT tap_values FROM unnest(taps) AS x(tap_values) ORDER
BY tap_values DESC LOOP
		IF last_tap_value IS NOT NULL THEN
			EXECUTE 'SELECT ' || last_tap_value || ' # GET_BIT(' || from_value
|| '::bit(' || bitlength || '), ' || tap.tap_values || '-1)' INTO
last_tap_value;
		ELSE
			EXECUTE 'SELECT GET_BIT(' || from_value || '::bit(' || bitlength ||
'), ' || tap.tap_values || '-1)' INTO last_tap_value;
			CONTINUE;
		END IF;
	END LOOP;

	new_value := (last_tap_value || SUBSTRING(from_value::BIT(bitlength),
1, bitlength - 1))::BIT(bitlength)::INT;

	RETURN new_value;
END;
$$ LANGUAGE plpgsql;

=# select get_lsfr(4,'{3,4}'::int[],6);
ERROR:  "S" is not a valid binary digit
LINE 1: SELECT 'SELECT ' || last_tap_value || ' # GET_BIT(' || from_...
               ^
QUERY:  SELECT 'SELECT ' || last_tap_value || ' # GET_BIT(' ||
from_value || '::bit(' || bitlength || '), ' || tap.tap_values ||
'-1)'
CONTEXT:  PL/pgSQL function "get_lsfr" line 12 at EXECUTE statement

http://pgsql.privatepaste.com/5441ff7cc0

I'm thinking maybe I haven't used the correct syntax.
-- 
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935

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