Bug #68600 [Opn->Nab]: shift

From:	requinix@php.net	Date:	Sat, 13 Dec 2014 08:31:53 +0000
Subject:	Bug #68600 [Opn->Nab]: shift
References:	1	Groups:	php.bugs
Request:	Send a blank email to php-bugs+get-189048@lists.php.net to get a copy of this message

Edit report at https://bugs.php.net/bug.php?id=68600&edit=1 ID: 68600 Updated by: requinix@php.net Reported by: armenhak59 at yahoo dot com Summary: shift -Status: Open +Status: Not a bug Type: Bug -Package: Compile Failure +Package: *General Issues Operating System: windows 7 32 bit PHP Version: 5.5.19 Block user comment: N Private report: N New Comment: Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php http://php.net/manual/en/language.operators.bitwise.php "Warning Shifting integers by values greater than or equal to the system long integer width results in undefined behavior. In other words, don't shift more than 31 bits on a 32-bit system, and don't shift more than 63 bits on a 64-bit system." This will change in PHP 7. https://wiki.php.net/rfc/integer_semantics "3. Left bitwise shifts by a number of bits beyond the bit width of an integer will always result in 0, even on CPUs which wrap around" Previous Comments: ------------------------------------------------------------------------ [2014-12-13 07:41:54] armenhak59 at yahoo dot com Description: ------------ <?php echo "SHIFT LEFT DO NOT WORKS RIGHT FOR NEGATIV NUMBER -1, BUT WORKS FOR OTHER NUMBERS "; $format = '%0' . 32 . "b "; $val = -1; echo " WRONG FOR -1 "; printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 32); $val = $val << 32; printf(' val = ' . $format, $val); echo " IT MUST BE "; printf('..... = ' . $format, 0); echo " FOR OTHER NUMBERS IT WORKS CORRECT:"; printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 1); $val = $val << 1; printf(' val = ' . $format, $val); printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 31); $val = $val << 31; printf(' val = ' . $format, $val); ?> Test script: --------------- <?php echo "SHIFT LEFT DO NOT WORKS RIGHT FOR NEGATIV NUMBER -1, BUT WORKS FOR OTHER NUMBERS "; $format = '%0' . 32 . "b "; $val = -1; echo " WRONG FOR -1 "; printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 32); $val = $val << 32; printf(' val = ' . $format, $val); echo " IT MUST BE "; printf('..... = ' . $format, 0); echo " FOR OTHER NUMBERS IT WORKS CORRECT:"; printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 1); $val = $val << 1; printf(' val = ' . $format, $val); printf(" val = %d String: %s = %d %s %d ", $val, 'res', $val, '<<', 31); $val = $val << 31; printf(' val = ' . $format, $val); ?> ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=68600&edit=1