Boyer-Moore string match algorithm

boyer-moore.php

<?php
 
define('ALPHABET_SIZE',1);
 
function compute_prefix($str,$size,&$result=0) 
{
    $result = $result[$size + 1];
    $q;
    $k;
    $result[0] = 0;
 
    $k = 0;
    for ($q = 1; $q < $size; $q++) 
    {
        while ($k > 0 && $str[$k] != $str[$q])
            $k = $result[$k-1];
 
        if ($str[$k] == $str[$q])
            $k++;
        $result[$q] = $k;
    }
}
 
function prepare_badcharacter_heuristic($str,$size,$result)
{
    $result = $result[ALPHABET_SIZE];
 
    $i = 0;
 
    for ($i = 0; $i < ALPHABET_SIZE; $i++)
        $result[$i] = -1;
 
    for ($i = 0; $i < $size; $i++)
        $result[(int) $str[$i]] = $i;
}
 
function prepare_goodsuffix_heuristic($normal, $size, &$result=1) 
{
    $result = $result[$size + 1];
    $left = (string) $normal;
    $right = $left + $size;
    $reversed[$size+1];
    $tmp = $reversed + $size;
    $i;
 
    /* reverse string */
    $tmp = 0;
    while ($left < $right)
        $tmp = $left++;
 
    $prefix_normal[$size];
    $prefix_reversed[$size];
 
    compute_prefix($normal, $size, $prefix_normal);
    compute_prefix($reversed, $size, $prefix_reversed);
 
    for ($i = 0; $i <= $size; $i++) 
    {
        $result[$i] = $size - $prefix_normal[$size-1];
    }
 
    for ($i = 0; $i < $size; $i++) 
    {
        $j = $size - $prefix_reversed[$i];
        $k = $i - $prefix_reversed[$i]+1;
 
        if ($result[$j] > $k) { $result[$j] = $k; }
    }
}
/*
 * Boyer-Moore search algorithm
 */
function boyermoore_search($haystack,$needle) {
    /*
     * Calc string sizes
     */
    $needle_len; 
    $haystack_len;
    $needle_len = strlen($needle);
    $haystack_len = strlen($haystack);
 
    /*
     * Simple checks
     */
    if($haystack_len == 0) { return NULL; }
    if($needle_len == 0) { return $haystack; }
 
    /*
     * Initialize heuristics
     */
    $badcharacter[ALPHABET_SIZE];
    $goodsuffix[$needle_len+1];
 
    prepare_badcharacter_heuristic($needle, $needle_len, $badcharacter);
    prepare_goodsuffix_heuristic($needle, $needle_len, $goodsuffix);
 
    /*
     * Boyer-Moore search
     */
    $s = 0;
    while($s <= ($haystack_len - $needle_len))
    {
        $j = $needle_len;
        while($j > 0 && $needle[$j-1] == $haystack[$s+$j-1])
            $j--;
 
        if($j > 0)
        {
            $k = $badcharacter[(int) $haystack[$s+$j-1]];
            $m;
            if($k < (int)$j && ($m = $j-$k-1) > $goodsuffix[$j])
                $s += $m;
            else
                $s += $goodsuffix[$j];
        }
        else
        {
            return $haystack + $s;
        }
    }
 
    return NULL;
}
?>

the code is error. can u explain it sir the each line of this code thanks you.