Question

I found this snippet of code online and I was wondering what it does:

$k[$i] = ord($key{$i}) & 0x1F;

I know that ord() returns an ASCII value, but I’m unclear on what the curly brackets do $key{$i} and also what this does & 0x1F.

Answer 1

That’s not an array syntax. It’s for accessing single characters from strings only. The index must be numeric.

 $str{1} == $str[1]

It’s briefly mentioned here in the info box: http://www.php.net/manual/en/language.types.string.php#language.types.string.substr

Also, it’s officially declared deprecated. It has been on and off supposed deprecation in the manual, but is still very valid, if uncommon, syntax.

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The & 0x1F is a bit-wise AND. In this case it limits the decimal values to 0 till 31.