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[The Little Guy]

I was looking over some php code, and came across this:

 

$c=($c*$j)<<2;

 

I have never see << before, what does it mean/do?

[xyph]

It's a bitwise operator for shifting bits to the left

 

http://php.net/manual/en/language.operators.bitwise.php

[ManiacDan]

<< and >> are bitwise operators.  They perform binary operations on integers.  In particular, this line takes $c, multiplies it by $j, and then multiplies that result by 8.  It's slightly faster to say $something << 3; than $something * 8;  It's leftover from C programmers who used it a lot.

 

-Dan

[The Little Guy]

how are 3 and 8 the same thing?

 

$something << 3;

$something * 8;

[Pandemikk]

how are 3 and 8 the same thing?

 

$something << 3;

$something * 8;

 

It's a bitwise operator for shifting bits to the left

 

http://php.net/manual/en/language.operators.bitwise.php

 

Read the article he linked. It was linked for a purpose. 3 and 8 are not the same. $x << 3 and $x * 8 are the same (essentially).

[KevinM1]

3 in this case means shifting the binary representation of the number 3 positions to the left.  That's the same as multiplying it by 2^3, or 8.

[xyph]

Here's what happens, step by step, if you're still confused

 

<?php 

// OUtput in plain text
header("Content-type: text/plain");

// Format is using 0 to pad the left side, 16 length, and binary
$format = '%016b';

$c = 5;
$j = 7;
echo '$c*$j:      '.sprintf($format,($c*$j))."\n";

echo '($c*$j)<<2: '.sprintf($format,(($c*$j)<<2))."\n";

echo 'Same as $c*$j with bits moved 2 to the left';

?>

 

$c*$j:      0000000000100011
($c*$j)<<2: 0000000010001100
Same as $c*$j with bits moved 2 to the left