PHP Hash algorithm: Times33 algorithm code example_PHP tutorial

PHP Hash algorithm: Times33 algorithm code example

This article mainly introduces the PHP Hash algorithm: Times33 algorithm code example. This article directly gives the implementation code. Friends who need it can refer to it. Next

I recently read a book and mentioned some Hash algorithms. What impressed me most was Times33. I didn’t understand it very well at the time, so I wrote a program today to verify it.

First enter the code:

Copy the code. The code is as follows:

　/**

　　* CRC32 Hash function

　　* @param $str

　　* @return int

　　*/

Function hash32($str)

　{

return crc32($str) >> 16 & 0x7FFFFFFF;

　}

　/**

　　* Times33 Hash function

　　* @param $str

　　* @return int

　　*/

Function hash33($str)

　{

　$hash = 0;

　for($i=0; $i

　$hash = 33 * $hash ord($str{$i});

　}

return $hash & 0x7FFFFFFF;

　}

　$n = 10;

// Test Case 1

　$stat = array();

　for($i=0; $i<10000; $i ){

　$str = substr(md5(microtime(true)), 0, 8);

　$p = hash32($str) % $n;

　if(isset($stat[$p])){

　$stat[$p] ;

　}else{

　$stat[$p] = 1;

　}

　}

print_r($stat);

// Test Case 2

　$stat = array();

　for($i=0; $i<10000; $i ){

　$str = substr(md5(microtime(true)), 0, 8);

　$p = hash33($str) % $n;

　if(isset($stat[$p])){

　$stat[$p] ;

　}else{

　$stat[$p] = 1;

　}

　}

print_r($stat);

There are two test cases above. The first one uses the CRC32 method; the second one is the Times33 algorithm implementation.

Effect:

The result distribution is similar between the two algorithms (it is probably a problem with the data source, md5 only has 0-f). There are also articles saying that CRC32 is more evenly distributed (reference link:)

But it is time consuming, CRC32 is nearly twice as fast as Times33.

Why 33?

It is a prime number (prime number) and an odd number. In addition to 33, there are 131, 1313, 5381, etc. PHP's built-in Hash function uses 5381, which was also mentioned in a blog post by "Brother Bird".