Short URL implement
Few months ago, I introduced a 易做图 algorithmthat allow users to implement their own short URL into their system. Today,I have some spare time so I decided to write the short URL algorithm'易做图mentation in PHP.
At first, we define a function called shorturl() thatreceives a URL as the input and returns anarray that contains 4 hashed values (each 6 characters).
function shorturl($input) { ... // return array of results}
Below is the original pseudocode:
... loop2: from 1st 4 bytes to 4th 4 bytes of md5 result cast the 4 bytes to an integer loop3: for shortCodeChar[0] to shortCodeChar[5] use 1st 5 bits of the integer to find the value in codeMap remove 5 bits from the integer end loop3 save shortCodeChar as shortCode ... // Database checking for duplication end loop2...The following code is written according to thealgorithm above excluding the database checking part for duplication:
[php] function shorturl($input) { $base32 = array ( 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5' ); $hex = md5($input); $hexLen = strlen($hex); $subHexLen = $hexLen / 8; $output = array(); for ($i = 0; $i < $subHexLen; $i++) { $subHex = substr ($hex, $i * 8, 8); $int = 0x3FFFFFFF & (1 * ('0x'.$subHex)); $out = ''; for ($j = 0; $j < 6; $j++) { $val = 0x0000001F & $int; $out .= $base32[$val]; $int = $int >> 5; } $output[] = $out; } return $output; } function shorturl($input) {
$base32 = array (
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p',
'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
'y', 'z', '0', '1', '2', '3', '4', '5'
);
$hex = md5($input);
$hexLen = strlen($hex);
$subHexLen = $hexLen / 8;
$output = array();
for ($i = 0; $i < $subHexLen; $i++) {
$subHex = substr ($hex, $i * 8, 8);
$int = 0x3FFFFFFF & (1 * ('0x'.$subHex));
$out = '';
for ($j = 0; $j < 6; $j++) {
$val = 0x0000001F & $int;
$out .= $base32[$val];
$int = $int >> 5;
}
$output[] = $out;
}
return $output;
}Sample code to test/use theabove function:
[php] $input = 'http://www.snippetit.com/1'; $output = shorturl($input); echo "Input : $input\n"; echo "Output : {$output[0]}\n"; echo " {$output[1]}\n"; echo " {$output[2]}\n"; echo " {$output[3]}\n"; echo "\n"; $input = 'http://www.snippetit.com/2'; $output = shorturl($input); echo "Input : $input\n"; echo "Output : {$output[0]}\n"; echo " {$output[1]}\n"; echo " {$output[2]}\n"; echo " {$output[3]}\n"; echo "\n"; $input = 'http://www.snippetit.com/1';
$output = shorturl($input);
echo "Input : $input\n";
echo "Output : {$output[0]}\n";
echo " {$output[1]}\n";
echo " {$output[2]}\n";
echo " {$output[3]}\n";
echo "\n";
$input = 'http://www.snippetit.com/2';
$output = shorturl($input);
echo "Input : $input\n";
echo "Output : {$output[0]}\n";
echo " {$output[1]}\n";
echo " {$output[2]}\n";
echo " {$output[3]}\n";
echo "\n";Output:
[plain] Input : http://www.snippetit.com/1 Output : h0xg4r bdr3tw osk2d3 4azfqa Input : http://www.snippetit.com/2 Output : tm5kxb ceoj2s yw3dvl nrmrxl Input : http://www.snippetit.com/1
Output : h0xg4r
bdr3tw
osk2d3
4azfqa
Input : http://www.snippetit.com/2
Output : tm5kxb
ceoj2s
yw3dvl
nrmrxlThe function return an array of 4 elements, youcan use any one of them. The others can be used as alternative unique code for the input when youfound a duplicated code in your database (same code but different input -although it is unlikely to happen but it will happen). Chances to get aduplicated code is about n/(32^6) or n/1,073,741,824 where n is the number of records in your database.
As you can see, the output results are quiterandom although you only have one character different in the input string. Theoutput is always consistent, for the same input you will always get the sameoutput.
To make the output more unpredictable by theothers, you can scramble the values in the $base32 array or/and add inyour ownprivate keyor/and XOR
补充：软件开发 , C语言 ,
