php-documentation-list | 2003101

[PHP-DOC] #25877 [Bgs->Opn]: >> operator bug for negative LOP From: moriyoshi <email protected>
Date: 10/15/03

 ID: 25877
 Updated by: moriyoshi <email protected>
 Reported By: cestmirl at freeside dot sk
-Status: Bogus
+Status: Open
 Bug Type: Documentation problem
 Operating System: Linux Debian, Win32
 PHP Version: 4.3.3
 New Comment:

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.

 

Previous Comments:
------------------------------------------------------------------------

[2003-10-15 12:57:34] cestmirl at freeside dot sk

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.

------------------------------------------------------------------------

[2003-10-15 11:54:01] jay <email protected>

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

------------------------------------------------------------------------

[2003-10-15 08:00:22] moriyoshi <email protected>

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

------------------------------------------------------------------------

[2003-10-15 07:56:56] moriyoshi <email protected>

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.

------------------------------------------------------------------------

[2003-10-15 07:40:14] cestmirl at freeside dot sk

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

------------------------------------------------------------------------ 

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