<?php
function BKDRHash($str)
{
$seed = 131; // 31 131 1313 13131 131313 etc..
$hash = 0;
$cnt = strlen($str);
for($i = 0; $i < $cnt; $i++)
{
$hash = ((floatval($hash * $seed) & 0x7FFFFFFF) + ord($str[$i])) & 0x7FFFFFFF;
}
return ($hash & 0x7FFFFFFF);
}
echo BKDRHash('ggsonic');//1471979560
echo BKDRHash('asdfasdfasdf123'); // 1220655578
?>
http://www.cnblogs.com/uvsjoh/archive/2012/03/27/2420120.html
http://www.daimami.com/php/198692.htm
另外 10万以内的数据量可以用 CRC32 (https://yq.aliyun.com/articles/2469)代替
crc32 冲突率测试报告 http://www.backplane.com/matt/crc64.html
生日攻击:http://baike.baidu.com/view/1474504.htm
有50%冲突概率 试验次数n大约为: 1.17sqr(N) N为hash 表范围