-
-
Save zdienos/3d450b75d58a3fed044dbfd5789ab01f to your computer and use it in GitHub Desktop.
Boyer-Moore string match algorithm
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
<?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; | |
} | |
?> |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment