Description:
------------
Bitwise shift right operator returns negative result (most significant
bit set) for negative input (left operand).

Following assert fails (though should NOT)

assert((1 << 31 >> 31) == 1);

Reproduce code:
---------------
assert((1 << 31 >> 31) == 1);

Actual result:
--------------
assertion failed

Since PHP doesn't support unsigned shift operations that are represented
by '<<<' or '>>>' in the C language, bit shift operations are done in
"sign-respectful" manner, where the most significant bit will never be
changed. This is expected behaviour, but not documented yet.

Heh, who told me that C supports '>>>' operator... there's no such
operator in that language.

This is expected. (1 << 31) wraps the 32-bit integer 
limit, and I believe this behaviour is undefined, at least 
in C and C++. If you run the same code in C or C++, the 
result is the same as what you're experiencing. 
 
J 

You're right, it's the same semantics as GCC or Java has for signed int
(though I've never experienced this yet as I've raised in Pascal
world...).

However, in this case, I think it's worth considering to implement Java
unsigned shift ops (<<<, >>>) in PHP. Of course, there's no problem to
mask out appropriate number of bits from left after making "signed
shift" right, but standard operator would be much cleaner solution.

You may want to see the following thread brought up in the past at the
php internals list:
http://marc.theaimsgroup.com/?l=php-dev&m=103530736509081&w=2

Anyway, Jay, do you think it is more than enough to add a slight comment
on the relevant page that the opeators cannot be used for unsigned
operation? I see no reason to bogusify this as I regard this as a
documentation problem.

 

Yeah, that would probably be a good idea. Maybe just a 
note that this sort of behaviour is undefined. We should 
probably check to see how it acts on Windows, too. (I 
don't have a Win box in front of me at the moment so if 
anybody could check...) 
 
J 

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation
better.

"Don't right shift for more than 32 bits on 32 bits systems. Don't left
shift in case it results to number longer than 32 bits."