PHP Efficient way to Convert String of Binary into Binary

Question

here is the skinny (scroll down to see the problem): I am doing Huffman Encoding to compress a file using PHP (for a project). I have made the map, and made everything into a string like so:

00101010001100001110011101001101111011111011

Now, I need to convert that into an actual binary string, in its current state, it is only a string of 1s and 0s.

Here is the problem:

The string of 1s and 0s is 17,747,595 characters long, and it is really slowing down at around 550,000

This is the code I have:

<?php

$i=0
$len = strlen($binaryString);

while ($i < $len){
    $section = substr($binaryString,$i,$i+8);
    $out .= chr(bindec($section));
    $i=$i+8;
}

?>

How can I make this efficient enough to run the 17 million character string?

Thanks very much for any support!

Did you take a look @ stackoverflow.com/questions/6382738/… — MagePal Extensions
– MagePal Extensions, Commented Nov 6, 2012 at 19:52
Don't write it to a variable in whole, but to some file cache after X bytes. That way, not the whole string is loaded on each iteration to append the next few bytes. — feeela
– feeela, Commented Nov 6, 2012 at 19:58
Yes, the original file being encoded is 4MB, and then broken out via Huffman to the 17m… I know there has to be an efficient way of doing this, I just dont know what it is lol. — Addo Solutions
– Addo Solutions, Commented Nov 6, 2012 at 19:59
why didnt you try to make bit stream instead of bit string? i mean just use 8 bit of the bye from the begining. it s because of locality of reference. — morteza kavakebi
– morteza kavakebi, Commented Nov 6, 2012 at 20:06

Baba · Accepted Answer · 2012-11-06 21:13:01Z

5

You don't need to loop you can use gmp with pack

$file = "binary.txt";
$string = file_get_contents($file);
$start = microtime(true);

// Convert the string
$string = simpleConvert($string);
//echo $string ;

var_dump(number_format(filesize($file),2),microtime(true)- $start);

function simpleConvert($string) {
    return pack('H*',gmp_strval(gmp_init($string, 2), 16));
}

Output

string '25,648,639.00' (length=13) <---- Length Grater than 17,747,595
float 1.0633520126343  <---------------- Total Conversion Time

Links

Note Solution requires GMP Functions

edited Nov 6, 2012 at 21:13

answered Nov 6, 2012 at 20:27

Baba

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3 Comments

Addo Solutions Over a year ago

Wow! I like that approach, but I seem to be getting a "Segmentation fault" upon initializing GMP in gmp_init($string, 2); any ideas what that is about? (Yes, I have GMP installed :)

Baba Over a year ago

What version of PHP & GMP ?

Addo Solutions Over a year ago

Ahh… I was running it on PHP/5.2.10 GD/4.1.4, but I moved it to my server with PHP/5.4.7 GMP/4.3.2 and it works like a charm :) Well done! Thanks @Baba

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