Created
February 24, 2012 19:31
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Boyer-Moore string match algorithm
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<?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; | |
} | |
?> |
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the code is error. can u explain it sir the each line of this code thanks you.