微博短链接算法php版本

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"    } }