php.net |  support |  documentation |  report a bug |  advanced search |  search howto |  statistics |  random bug |  login

go to bug id or search bugs for

Bug #68600 shift
Submitted: 2014-12-13 07:41 UTC Modified: 2014-12-13 08:31 UTC
From: armenhak59 at yahoo dot com Assigned:
Status: Not a bug Package: *General Issues
PHP Version: 5.5.19 OS: windows 7 32 bit
Private report: No CVE-ID: None
View Developer Edit
 [2014-12-13 07:41 UTC] armenhak59 at yahoo dot com 
Description:
------------
<?php
echo "SHIFT LEFT DO NOT WORKS RIGHT FOR NEGATIV NUMBER -1, BUT WORKS FOR OTHER NUMBERS<br><br>";
   $format = '%0' . 32 . "b<br>";
    $val = -1;
echo "<br> WRONG FOR -1<br>";
 printf(" val = %d String: %s = %d %s %d<br>", $val, 'res', $val, '<<', 32);
  $val = $val << 32;
  printf(' val = ' . $format, $val);
   echo "<br>  IT MUST BE <br>";
 printf('..... = ' . $format, 0);
echo "<br><br><br>FOR OTHER NUMBERS IT WORKS CORRECT:";
 printf("<br><br>  val = %d String: %s = %d %s %d<br>", $val, 'res', $val, '<<', 1);
  $val = $val << 1;
 printf('  val = ' . $format, $val);
 printf("<br><br>  val = %d String: %s = %d %s %d<br>", $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<br><br>";
   $format = '%0' . 32 . "b<br>";
    $val = -1;
echo "<br> WRONG FOR -1<br>";
 printf(" val = %d String: %s = %d %s %d<br>", $val, 'res', $val, '<<', 32);
  $val = $val << 32;
  printf(' val = ' . $format, $val);
   echo "<br>  IT MUST BE <br>";
 printf('..... = ' . $format, 0);
echo "<br><br><br>FOR OTHER NUMBERS IT WORKS CORRECT:";
 printf("<br><br>  val = %d String: %s = %d %s %d<br>", $val, 'res', $val, '<<', 1);
  $val = $val << 1;
 printf('  val = ' . $format, $val);
 printf("<br><br>  val = %d String: %s = %d %s %d<br>", $val, 'res', $val, '<<', 31);
 $val = $val << 31;
  printf(' val = ' . $format, $val);
?>

Patches

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2014-12-13 08:31 UTC] requinix@php.net
-Status: Open +Status: Not a bug -Package: Compile Failure +Package: *General Issues
 [2014-12-13 08:31 UTC] requinix@php.net 
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"
 
PHP Copyright © 2001-2026 The PHP Group
All rights reserved. 		Last updated: Wed Oct 07 19:00:01 2026 UTC