#25877 [Bgs->Opn]: >> operator bug for negative LOP

ID: 25877 Updated by: moriyoshi@php.net 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@php.net 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@php.net Heh, who told me that C supports '>>>' operator... there's no such operator in that language. ------------------------------------------------------------------------ [2003-10-15 07:56:56] moriyoshi@php.net 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 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/?id=25877&edit=1