The original snippet does not work anymore, because of the deprecated 'prototyped' keyword. Below is an updated version, that can also be found online.

.sub hex2decimal 
    .param string hex
    .local int result
    .local int position
    .local string digits
    .local int len
    result = 0
    position = 0
    digits = '0123456789ABCDEF'
    upcase hex
    len = length hex
p_hex_loop:
    if position == len goto p_hex_over
    result *= 16
    $S1 = hex[position]
    $I1 = index digits, $S1
    result += $I1
    inc position
    goto p_hex_loop
    
p_hex_over:
    .return(result)
.end


.sub url_decode 
    .param string theURL
    .local int position
    # + becomes space
p_unesc_url_space:
    position = index theURL, '+'
    if position == -1 goto p_unesc_url_others_0
    theURL[position] = ' '
    goto p_unesc_url_space
p_unesc_url_others_0:
    position = 0
p_unesc_url_others:
    position = index theURL, '%', position
    if position == -1 goto p_unesc_url_over
    $I1 = position + 1
    $S1 = substr theURL, $I1, 2
    $I1 = hex2decimal($S1)
    $S1 = chr $I1
    theURL = substr position, 3, $S1 
    inc position
    goto p_unesc_url_others
p_unesc_url_over:
    .return(theURL)
.end



.sub get_query_params 
    .param string query
    .local pmc result
    result = new .Hash
    
    
    .local int start
    .local int end
    .local int len
    .local string key
    .local string value
    start = 0
parse:    
    index end, query, '=', start
    if end == -1 goto ret
    len = end - start 
    substr key, query, start, len
    key = url_decode(key)
    start = end + 1
    index end, query, '&', start
    if end > -1 goto more_data
        substr value, query, start
        value = url_decode(value)
        result[key] = value
        goto ret
    more_data:
        len = end - start
        substr value, query, start, len
        value = url_decode(value)
        result[key] = value
        start = end + 1
        goto parse
ret:
    
    .return(result)
    
.end
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