show binary string in form of bits in php

Question

I have this code:

$a = pack('N',0b00111010000011110101011100100010);

$start = strlen($a)*8 -1;
$str = '';
for($k = $start; $k>=0; $k--) {
    $bit = ($a >> $k) & 1;
    $str .= $bit;
}

var_dump($str);

output must be this:

00111010000011110101011100100010

but show me this output:

00000000000000000000000000000000

what is wrong in this code ??

Timo Schwarzer · Accepted Answer · 2014-12-06 21:23:15Z

1

There is a typo.

$a = pack('N',0b00111010000011110101011100100010);
               ^

answered Dec 6, 2014 at 21:23

Timo Schwarzer

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Comments

saeid ezzati · Accepted Answer · 2014-12-06 21:37:46Z

0

I changed code to this and my problem solved:

$a = pack('N',0b00111010000011110101011100100010);

$str = '';
for($j=0;$j<strlen($a); $j++) {
    $byte = substr($a, $j, 1);
    $num = ord($byte);
    for($k=7; $k>=0; $k--) {
        $bit = ($num >> $k) & 1;
        $str .= $bit;

    }

}
var_dump($str);

answered Dec 6, 2014 at 21:37

saeid ezzati

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Comments

Andras · Accepted Answer · 2014-12-07 00:30:00Z

0

another way is to shift the bit you're reading instead of the data byte, same thing really. No need to substr() a single byte, array subscript notation works

$a = pack('N',0b00111010000011110101011100100010);
$str = '';
for ($i=0; $i<strlen($a); $i++) {
    $byte = ord($a[$i]);
    $mask = 0x80;
    while ($mask > 0) {
        $str .= ($byte & $mask) ? '1' : '0';
    }
}

echo "$str\n";

Edit: fixed typos, now runs

edited Dec 7, 2014 at 0:30

answered Dec 6, 2014 at 22:48

Andras

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2 Comments

saeid ezzati Over a year ago

your code execution time is very long. in my browser its time was infinite and finaly finished with overflow memory size !! but execution time of my solution is about 1 second.

Andras Over a year ago

oops, had two bugs in there. try now. Don't know why it would not have exited, though, on my system it immediately errored out.

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