Weibo short link algorithm PHP version implementation code_PHP tutorial

Idea:
1) Generate a 32-bit signature string from md5 of the long URL, divided into 4 segments, each segment is 8 bytes;
2) Process these four segments in a loop, take 8 bytes, and read them into a hexadecimal string and operate with 0x3fffffff (30 bits 1), that is, more than 30 bits are ignored;
3) These 30 bits are divided into 6 segments, and each 5-digit number is used as an index of the alphabet to obtain a specific character, in sequence Get a 6-digit string;
4) The total md5 string can get 4 6-digit strings; any one of them can be used as the short URL address of this long URL;
The following is the PHP code:

Copy code The code is as follows:

function shorturl($url='', $prefix='', $suffix='' ) {
$base = 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') ;
$hex = md5($prefix.$url.$suffix);
$hexLen = strlen($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 .= $base[$val];
$int = $int >> 5;
}
$output[] = $out;
}
return $output;
}
$urls = shorturl('http://www.jb51.net/');
var_dump($urls);

Result

Copy code The code is as follows:

array(4) {
[0]=>
string(6) "alms1l"
[1]=>
string(6) "2ipmby"
[2]=>
string(6) "avo1hu"
[ 3]=>
string(6) "fdlban"
}

Another version:

Copy code The code is as follows:

function shorturl($url='', $prefix='', $suffix='') {
$base = 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",
"6","7","8"," 9","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");
$hex = md5($prefix.$url.$suffix);
$hexLen = strlen($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 = 0x0000003D & $int;
$out .= $base[$val];
$int = $int >> 5;
}
$output[] = $out;
}
return $output;
}

Result:

Copy the code The code is as follows:

array(4) {
[0] =>
string(6) "6jmMVj"
[1] =>
string(6) "2EnIby"
[2] =>
string(6) "6vIVfu"
[3] =>
string(6) "B7Fb6n "
}

But the collision rate of the upgraded version is higher, I don’t know why.
Test code for testing collision:

Copy code The code is as follows:

$result = array();
$repeats= array();
$loop = 20000;
for($i=0;$i<$loop;$i++){
$url = 'http://www.jb51 .net/?id='.$i;
$shorta = shorturl($url);
$short = $shorta[0];
if(in_array($short, $result)){
$repeats[] = $short;
}
$result[] = $short;
}
$result = array();
for($i=0; $i<$loop;$i++){
$url = 'http://www.jb51.net/?id='.$i;
$shorta = shorturl($url);
$short = $shorta[0];
if(in_array($short, $repeats)){
$result[$short][] = $url;
}
}
var_dump($repeats);
var_dump($result);

Result:

Copy code The code is as follows:

array(8) {
[0] =>
string(6) "3eQBzq"
[1] =>
string(6) "uQFnay"
[2] =>
string(6) "qEZbIv"
[3] =>
string(6) "fMneYf"
[4] =>
string(6) "FJj6Fr"
[5] =>
string(6) "3Eviym"
[6] =>
string(6) "j2mmuy"
[7] =>
string(6) "jyQfIv"
}
array(8) {
'jyQfIv' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=1640"
[1] =>
string(27) "http://www.jb51.net/?id=18661"
}
'fMneYf' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=2072"
[1] =>
string(26) "http://www.jb51.net/?id=8480"
}
'3eQBzq' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=4145"
[1] =>
string(26) "http://www.jb51.net/?id=4273"
}
'j2mmuy' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=7131"
[1] =>
string(27) "http://www.jb51.net/?id=17898"
}
'qEZbIv' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=7320"
[1] =>
string(26) "http://www.jb51.net/?id=8134"
}
'uQFnay' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=7347"
[1] =>
string(26) "http://www.jb51.net/?id=7962"
}
'FJj6Fr' =>
array(2) {
[0] =>
string(26) "http://www.jb51.net/?id=8628"
[1] =>
string(26) "http://www.jb51.net/?id=9031"
}
'3Eviym' =>
array(2) {
[0] =>
string(27) "http://www.jb51.net/?id=11175"
[1] =>
string(27) "http://www.jb51.net/?id=14437"
}
}

http://www.bkjia.com/PHPjc/325982.htmlwww.bkjia.comtruehttp://www.bkjia.com/PHPjc/325982.htmlTechArticle思路： 1)将长网址md5生成32位签名串,分为4段, 每段8个字节; 2)对这四段循环处理, 取8个字节, 将他看成16进制串与0x3fffffff(30位1)与操作, 即超过...