Google PageRank的计算源代码_互联网十年风云录

　　最近对google的PageRank(网页等级)比较感兴趣，一直想知道如何不用google toolbar来获取pr值。苦苦搜索之后,找到如下代码:

<?php

/**

This code is released unto the public domain

*/

//header("Content-Type: text/plain; charset=utf-8");

define('GOOGLE_MAGIC', 0xE6359A60);

//unsigned shift right

function zeroFill($a, $b)

{

    $z = hexdec(80000000);

        if ($z & $a)

        {

            $a = ($a>>1);

            $a &= (~$z);

            $a |= 0x40000000;

            $a = ($a>>($b-1));

        }

        else

        {

            $a = ($a>>$b);

        }

        return $a;

}

function mix($a,$b,$c) {

$a -= $b; $a -= $c; $a ^= (zeroFill($c,13));

$b -= $c; $b -= $a; $b ^= ($a<<8);

$c -= $a; $c -= $b; $c ^= (zeroFill($b,13));

$a -= $b; $a -= $c; $a ^= (zeroFill($c,12));

$b -= $c; $b -= $a; $b ^= ($a<<16);

$c -= $a; $c -= $b; $c ^= (zeroFill($b,5));

$a -= $b; $a -= $c; $a ^= (zeroFill($c,3));

$b -= $c; $b -= $a; $b ^= ($a<<10);

$c -= $a; $c -= $b; $c ^= (zeroFill($b,15));

return array($a,$b,$c);

}

function GoogleCH($url, $length=null, $init=GOOGLE_MAGIC) {

    if(is_null($length)) {

        $length = sizeof($url);

    }

    $a = $b = 0x9E3779B9;

    $c = $init;

    $k = 0;

    $len = $length;

    while($len >= 12) {

        $a += ($url[$k+0] +($url[$k+1]<<8) +($url[$k+2]<<16) +($url[$k+3]<<24));

        $b += ($url[$k+4] +($url[$k+5]<<8) +($url[$k+6]<<16) +($url[$k+7]<<24));

        $c += ($url[$k+8] +($url[$k+9]<<8) +($url[$k+10]<<16)+($url[$k+11]<<24));

        $mix = mix($a,$b,$c);

        $a = $mix[0]; $b = $mix[1]; $c = $mix[2];

        $k += 12;

        $len -= 12;

    }

    $c += $length;

    switch($len)              /* all the case statements fall through */

    {

        case 11: $c+=($url[$k+10]<<24);

        case 10: $c+=($url[$k+9]<<16);

        case 9 : $c+=($url[$k+8]<<8);

          /* the first byte of c is reserved for the length */

        case 8 : $b+=($url[$k+7]<<24);

        case 7 : $b+=($url[$k+6]<<16);

        case 6 : $b+=($url[$k+5]<<8);

        case 5 : $b+=($url[$k+4]);

        case 4 : $a+=($url[$k+3]<<24);

        case 3 : $a+=($url[$k+2]<<16);

        case 2 : $a+=($url[$k+1]<<8);

        case 1 : $a+=($url[$k+0]);

         /* case 0: nothing left to add */

    }

    $mix = mix($a,$b,$c);

    /*-------------------------------------------- report the result */

    return $mix[2];

}

//converts a string into an array of integers containing the numeric value of the char