微博短链接算法php版本实现代码

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:
<div class="codetitle"><a style="CURSOR: pointer" data="2038" class="copybut" id="copybut2038" onclick="doCopy('code2038')"> 代码如下:<div class="codebody" id="code2038">
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;
}
$urls = shorturl('//www.52php.cn/');
var_dump($urls);

结果
<div class="codetitle"><a style="CURSOR: pointer" data="93752" class="copybut" id="copybut93752" onclick="doCopy('code93752')"> 代码如下:<div class="codebody" id="code93752">
array(4) {
[0]=>
string(6) "alms1l"
[1]=>
string(6) "2ipmby"
[2]=>
string(6) "avo1hu"
[3]=>
string(6) "fdlban"
}

另外一个版本：
<div class="codetitle"><a style="CURSOR: pointer" data="71725" class="copybut" id="copybut71725" onclick="doCopy('code71725')"> 代码如下:<div class="codebody" id="code71725">
function shorturl($url='',$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,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：
<div class="codetitle"><a style="CURSOR: pointer" data="11246" class="copybut" id="copybut11246" onclick="doCopy('code11246')"> 代码如下:<div class="codebody" id="code11246">
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：
<div class="codetitle"><a style="CURSOR: pointer" data="92684" class="copybut" id="copybut92684" onclick="doCopy('code92684')"> 代码如下:<div class="codebody" id="code92684">
$result = array();
$repeats= array();
$loop = 20000;
for($i=0;$i<$loop;$i++){
$url = '//www.52php.cn/?id='.$i;
$shorta = shorturl($url);
$short = $shorta[0];
if(in_array($short,$result)){
$repeats[] = $short;
}
$result[] = $short;
}
$result = array();
for($i=0;$i<$loop;$i++){
$url = '//www.52php.cn/?id='.$i;
$shorta = shorturl($url);
$short = $shorta[0];
if(in_array($short,$repeats)){
$result[$short][] = $url;
}
}
var_dump($repeats);
var_dump($result);

结果：
<div class="codetitle"><a style="CURSOR: pointer" data="74930" class="copybut" id="copybut74930" onclick="doCopy('code74930')"> 代码如下:<div class="codebody" id="code74930">
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) "//www.52php.cn/?id=1640"
[1] =>
string(27) "//www.52php.cn/?id=18661"
}
'fMneYf' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=2072"
[1] =>
string(26) "//www.52php.cn/?id=8480"
}
'3eQBzq' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=4145"
[1] =>
string(26) "//www.52php.cn/?id=4273"
}
'j2mmuy' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=7131"
[1] =>
string(27) "//www.52php.cn/?id=17898"
}
'qEZbIv' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=7320"
[1] =>
string(26) "//www.52php.cn/?id=8134"
}
'uQFnay' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=7347"
[1] =>
string(26) "//www.52php.cn/?id=7962"
}
'FJj6Fr' =>
array(2) {
[0] =>
string(26) "//www.52php.cn/?id=8628"
[1] =>
string(26) "//www.52php.cn/?id=9031"
}
'3Eviym' =>
array(2) {
[0] =>
string(27) "//www.52php.cn/?id=11175"
[1] =>
string(27) "//www.52php.cn/?id=14437"
}
}

（编辑：李大同）

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