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LZW compression: Difference between revisions
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<pre>
T O B E O R N O T 256 258 260 265 259 261 263
TOBEORNOTTOBEORTOBEORNOT
</pre>
=={{header|PHP}}==
{{trans|Javascript}}
<lang PHP>function LZW_com($unc) {
$i;$c;$wc;
$w = "";
$dictionary = array();
$result = array();
$dictSize = 256;
for ($i = 0; $i < 256; $i += 1) {
$dictionary[chr($i)] = $i;
}
for ($i = 0; $i < strlen($unc); $i++) {
$c = $unc[$i];
if (property_exists($dictionary, $w.$c)) {
$w = $w.$c;
} else {
array_push($result,$dictionary[$w]);
$dictionary[$wc] = $dictSize++;
$w = (string)$c;
}
}
if ($w !== "") {
array_push($result,$dictionary[$w]);
}
array_shift($result);
return implode(",",$result);
}
function LZW_ext($com) {
$com = explode(",",$com);
$i;$w;$k;$result;
$dictionary = array();
$entry = "";
$dictSize = 256;
for ($i = 0; $i < 256; $i++) {
$dictionary[$i] = chr($i);
}
$w = chr($com[0]);
$result = $w;
for ($i = 1; $i < count($com);$i++) {
$k = $com[$i];
if ($dictionary[$k]) {
$entry = $dictionary[$k];
} else {
if ($k === $dictSize) {
$entry = $w.$w[0];
} else {
return null;
}
}
$result .= $entry;
$dictionary[$dictSize++] = $w + $entry[0];
$w = $entry;
}
return $result;
}
//How to use
$str = 'TOBEORNOTTOBEORTOBEORNOT';
$lzw = new LZW();
$com = $lzw->compress($str);
$dec = $lzw->decompress($com);
echo $com . "<br>" . $dec;
</lang>
{{out}}
<pre>
84,79,66,69,79,82,78,79,84,84,79,66,69,79,82,84,79,66,69,79,82,78,79,84
TOBEORNOTTOBEORTOBEORNOT
</pre>
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