Base58 Encoder function in PostgreSQL

I found this MySQL function for Base58 Encoder in a Github Gist.

DELIMITER $$

CREATE FUNCTION base58_encode (num int) RETURNS varchar(255)
  DETERMINISTIC

BEGIN
  DECLARE alphabet varchar(255);
  DECLARE base_count int DEFAULT 0;
  DECLARE encoded varchar(255);
  DECLARE divisor DECIMAL(10,4);
  DECLARE mode int DEFAULT 0;

  SET alphabet = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ';
  SET base_count = CHAR_LENGTH(alphabet);
  SET encoded = "";

  WHILE num  >= base_count DO
    SET divisor = num / base_count;
    SET mode = (num - (base_count* TRUNCATE(divisor,0)));
    SET encoded = CONCAT(SUBSTRING(alphabet FROM mode+1 FOR 1), encoded);
    SET num = TRUNCATE(divisor,0);
  END WHILE;

  SET encoded = CONCAT(SUBSTRING(alphabet FROM num+1 FOR 1), encoded);

  RETURN (encoded);

END

I am new to PostgreSQL and having difficulty converting above function to PostgreSQL function.

How would be the equivalent PostgreSQL function of above SQL snippet for Base58 Encoder?

Equivalent function in PostgreSQL that I came up with is as follows.

CREATE FUNCTION base58_encode(num INT)
  RETURNS VARCHAR(255) AS $encoded$

DECLARE
  alphabet   VARCHAR(255);
  base_count INT DEFAULT 0;
  encoded    VARCHAR(255);
  divisor    DECIMAL(10, 4);
  mod        INT DEFAULT 0;

BEGIN
  alphabet := '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ';
  base_count := char_length(alphabet);
  encoded := '';

  WHILE num >= base_count LOOP
    divisor := num / base_count;
    mod := (num - (base_count * trunc(divisor, 0)));
    encoded := concat(substring(alphabet FROM mod + 1 FOR 1), encoded);
    num := trunc(divisor, 0);
  END LOOP;

  encoded = concat(substring(alphabet FROM num + 1 FOR 1), encoded);

  RETURN (encoded);

END; $encoded$
LANGUAGE PLPGSQL;