Micro-blog Short link algorithm php version

1) will be a long URL MD5 generated 32-bit signature string, divided into 4 paragraphs, 8 bytes per paragraph;

2 The four-segment loop is processed, and 8 bytes are taken, which he sees as the 16-string and 0X3FFFFFFF ( 30-bit 1) with operations, that is, more than 30 bits of ignored processing;

3) This 30-bit is divided into 6 segments, each 5-digit number takes a specific character as the index of the alphabet, and sequentially obtains a 6-bit string;

4) The total MD5 string can get 4 6-bit strings ; take any one inside to serve as a short URL for this long URL;

The following is PHP code:

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 '); /p>

$hex = MD5 ($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;/p>

$out. = $base 32[$val];

$int = $int >> 5;

}

$output [] = $out;

}

return $output;

}

$urls = Shorturl (' http://www.php100.com ');

Var_dump ($urls);