Regex Replace with 2 conditions

Hi all,

Is there a way to specify 2 conditions in regexp_replace?
I need an SQL function that eliminates all ASCII characters from 1-255 that are not A-Z, a-z, 0-9, and special characters % and _ so something like:

SELECT regexp_replace(p_string, E'[' || CHR(1) || '-' || CHR(255) || '&&[^A-Za-z0-9%_]]', '', 'g'));

But this syntax is not really working.

I have written a SQL function that achieves this, but I am not happy with it because it is hard to read and maintain:

-- Eliminates all ASCII characters from 1-255 that are not A-z, a-z, 0-9, and special characters % and _
-- The computed regex expression that is between E[] is CHR(1)-$&-/:-(at)[-^`{-ÿ](dot)
CREATE OR REPLACE FUNCTION testFunction(p_string CHARACTER VARYING) RETURNS VARCHAR AS $$
SELECT regexp_replace(p_string, E'[' || CHR(1) || '-' || CHR(36) || CHR(38) || '-' || CHR(47) || CHR(58) || '-' || CHR(64) || CHR(91) || '-' || CHR(94) || CHR(96) || CHR(123) || '-' || CHR(255) || ']', '', 'g');
$$ LANGUAGE sql IMMUTABLE;

Please help me figure out how to achieve this.

Thanks a lot,
Denisa Cîrstescu