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30位的忽略处理;

3)这30位分成6段, 每5位的数字作为字母表的索引取得特定字符, 依次进行获得6位字符串;

4)总的md5串可以获得4个6位串; 取里面的任意一个就可作为这个长url的短url地址;

下面是PHP代码:

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('https://www.jb51.net/');

var_dump($urls);

结果

array(4) {

[0]=>

string(6) "alms1l"

[1]=>

string(6) "2ipmby"

[2]=>

string(6) "avo1hu"

[3]=>

string(6) "fdlban"

}

另外一个版本：

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;

}

结果：

array(4) {

[0] =>

string(6) "6jmMVj"

[1] =>

string(6) "2EnIby"

[2] =>

string(6) "6vIVfu"

[3] =>

string(6) "B7Fb6n"

}

但是升级版本碰撞率反而更高了，不知道为什么。

测试碰撞的测试代码：

$result = array();

$repeats= array();

$loop = 20000;

for($i=0;$i

$url = 'https://www.jb51.net/?id='.$i;

$shorta = shorturl($url);

$short = $shorta[0];

if(in_array($short, $result)){

$repeats[] = $short;

}

$result[] = $short;

}

$result = array();

for($i=0;$i

$url = 'https://www.jb51.net/?id='.$i;

$shorta = shorturl($url);

$short = $shorta[0];

if(in_array($short, $repeats)){

$result[$short][] = $url;

}

}

var_dump($repeats);

var_dump($result);

结果：

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) "https://www.jb51.net/?id=1640"

[1] =>

string(27) "https://www.jb51.net/?id=18661"

}

'fMneYf' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=2072"

[1] =>

string(26) "https://www.jb51.net/?id=8480"

}

'3eQBzq' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=4145"

[1] =>

string(26) "https://www.jb51.net/?id=4273"

}

'j2mmuy' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=7131"

[1] =>

string(27) "https://www.jb51.net/?id=17898"

}

'qEZbIv' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=7320"

[1] =>

string(26) "https://www.jb51.net/?id=8134"

}

'uQFnay' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=7347"

[1] =>

string(26) "https://www.jb51.net/?id=7962"

}

'FJj6Fr' =>

array(2) {

[0] =>

string(26) "https://www.jb51.net/?id=8628"

[1] =>

string(26) "https://www.jb51.net/?id=9031"

}

'3Eviym' =>

array(2) {

[0] =>

string(27) "https://www.jb51.net/?id=11175"

[1] =>

string(27) "https://www.jb51.net/?id=14437"

}

}