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Subject: Shifting bits of a binary string
From: php@marc-bennewitz.de (Marc Bennewitz)

Hi List,

I hope I'm on the right list but I can't find any other helpful.

I have a binary string and I would like to work with bitwise operators.
The only help I found was to convert it to an integer. That's ok but it 
results in some questions:

  - What if the binary data is more than 32/64 bits long?
  - Why converting binary data of form one into binary data of another 
form only to manipulate bits?

So I simply tested what's going on if I operate on a string directly but 
on shifting I get the same wrong result every time.
(Testscript below)

On reading the manual the only note for strings are the following:
(http://www.php.net/manual/en/language.operators.bitwise.php)
 > Be aware of data type conversions. If both the left-hand and 
right-hand parameters are strings, the bitwise operator will operate on 
the characters' ASCII values.

Why such bit operators doesn't work with strings?
Why there is not helpful information about in the manual.
Why on operation something not working doesn't result in an error/notice 
but in a completely unexpected value?

Greetings
Marc


Shift to the left:
var_dump(decbin(ord(chr(1))));
for ($i=0; $i<10; $i++) {
     var_dump(decbin(ord(chr(1) << $i)));
}

Output:
string(1) "1"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"

Shift to the right:
var_dump(decbin(ord(chr(32))));
for ($i=0; $i<10; $i++) {
     var_dump(decbin(ord(chr(32) >> $i)));
}

Output:
string(1) "100000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"
string(6) "110000"