Weibo short link algorithm PHP version implementation code _php tutorial

Ideas:
1) to generate a long URL MD5 32-bit signature string, divided into 4 segments, 8 bytes per segment;
2) for this four-segment cycle processing, take 8 bytes, he is regarded as 16 binary string and 0X3FFFFFFF (30 bit 1) and operation, that is, more than 30 bits of ignoring processing;
3) The 30 bits are divided into 6 segments, and each 5 digit number is taken as an index of the alphabet to obtain a specific character, followed by a 6-bit string;
4) The total MD5 string can obtain 4 6-bit strings; Take any one inside to be the short URL address for this long URL;
Here is the PHP code:
Copy CodeThe code is as follows:
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;
}
$urls = Shorturl (' http://www.jb51.net/');
Var_dump ($urls);

Results
Copy CodeThe code is as follows:
Array (4) {
[0]=>
String (6) "alms1l"
[1]=>
String (6) "2ipmby"
[2]=>
String (6) "Avo1hu"
[3]=>
String (6) "Fdlban"
}

A different version:
Copy CodeThe code is as follows:
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;
}

Results:
Copy CodeThe code is as follows:
Array (4) {
[0] = =
String (6) "6jmMVj"
[1] = =
String (6) "2EnIby"
[2] = =
String (6) "6vIVfu"
[3] = =
String (6) "b7fb6n"
}

But the upgrade version of the collision rate is even higher, do not know why.
Test code for testing collisions:
Copy CodeThe code is as follows:
$result = Array ();
$repeats = Array ();
$loop = 20000;
for ($i =0; $i < $loop; $i + +) {
$url = ' http://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 < $loop; $i + +) {
$url = ' http://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);

Results:
Copy CodeThe code is as follows:
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 ("http://www.jb51.net/?id=1640")
[1] = =
String ("http://www.jb51.net/?id=18661")
}
' Fmneyf ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=2072")
[1] = =
String ("http://www.jb51.net/?id=8480")
}
' 3eQBzq ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=4145")
[1] = =
String ("http://www.jb51.net/?id=4273")
}
' J2mmuy ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=7131")
[1] = =
String ("http://www.jb51.net/?id=17898")
}
' Qezbiv ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=7320")
[1] = =
String ("http://www.jb51.net/?id=8134")
}
' Uqfnay ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=7347")
[1] = =
String ("http://www.jb51.net/?id=7962")
}
' Fjj6fr ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=8628")
[1] = =
String ("http://www.jb51.net/?id=9031")
}
' 3Eviym ' =
Array (2) {
[0] = =
String ("http://www.jb51.net/?id=11175")
[1] = =
String ("http://www.jb51.net/?id=14437")
}
}

http://www.bkjia.com/PHPjc/325982.html www.bkjia.com true http://www.bkjia.com/PHPjc/325982.html techarticle ideas: 1) The long URL MD5 generated 32-bit signature string, divided into 4 segments, 8 bytes per segment; 2) for this four-segment loop processing, take 8 bytes, and treat him as 16 binary string with 0X3FFFFFFF (30 bit 1) with operation, ie over ...

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