微博短链接算法php版本

来源：互联网发布：知无尽而学无涯编辑：程序博客网时间：2024/06/04 19:48

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;} $urls = shorturl('http://www.hdj.me/');var_dump($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：

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

结果：

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