This is driving me mad. I have a perl script that has been working for several months but the other day it broke (the script hasn't been modified since I first wrote it). At first I thought, "well, it must be a result of something I did elsewhere that's mucking up the input to the script", but when I looked closer I realized that a bitwise & was now failing to work properly.

In the script I have a function that hashes a string to a 32-bit value. It looks like this:

sub MakeHashString($)
   {
   my $string = shift;
   my $hash = 0;
   my $i = 0;
   my $c = 0;

   for ($i = 0; $i < length($string); ++$i)
       {
       $c = ord(substr($string, $i, 1));
       $hash = ($c + ($hash * 64) + ($hash * 65536) - $hash) & 0xfffff
+fff;
       }

   return $hash;
   }

[download]

I added prints to the function to isolate the problem. When this function gets called with, for example, the string "accept", here is what $c and $hash are at the end of each loop iteration, showing $hash before and after the "& 0xffffffff":

c = 97, hash = 97 masked hash  = 97
c = 99, hash = 6363202 masked hash  = 6363202
c = 99, hash = 417419688097 masked hash  = 4294967295
c = 101, hash = 281745559584806 masked hash  = 4294967295
c = 112, hash = 281745559584817 masked hash  = 4294967295
c = 116, hash = 281745559584821 masked hash  = 4294967295

[download]

After the third iteration, $hash exceeds 0xffffffff and is forevermore relegated to being masked to a result of 0xffffffff. It doesn't matter if I mask it with the base 10 literal instead (i.e., 4294967295).

As I said, this script has worked fine for ages. My only thought was that perhaps my system path got messed up and a different version of perl is running. The version of perl I'm running which produces this issue is:

This is perl, v5.8.8 built for MSWin32-x86-multi-thread
(with 50 registered patches, see perl -V for more detail)

Copyright 1987-2006, Larry Wall

[download]

Anyone have an idea as to why bitwise & would fail like this?

Update: The perl version is ActiveState's build.

In reply to Bitwise & stopped working? by Krokus

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