My application involves data storted in a database, one field of which is a bitmapped value.

The user-defined routines provided by one of our team members uses these values correctly, to process the records in various ways.

But some queries need to look up a bit-field, alter it, and use the result in a new query.

SQL doesn't do bit-fields, so I have to do it in Perl.

I do something like this .. 

$bitfield = ....
my @fields = ( $modifier =~ m{ ([+-])  (\d+) }gxms ); # extract mods
while ( @fields >= 2 ) {                # for each modification
    my $op    = shift @fields;
    my $value = shift @fields;

    if ( $op eq '+') {
        $bitfield |= $value;            # set a bit w/ OR
    }
    elsif ($op eq '-' ) {
        my $dummy;                      # no-op to force full-width
        $dummy = sprintf "%064b\n", $value;
        my $negated = ~$value;
        $trade_condition &= $negated    # clear a bit w/ negated AND
    }
}

[download]

I put in the sprintf because it cleared up a problem that negating one produced zero.

But I still have a problem that starting off with a $bitfield value of one and modifying it with $modifier = '+2+16+1024' produces 3562 when I'm not looking, or 1043 when I single-step through it. Actually, single-stepping isn't enough, I need to be observing. Using

 > printf "064b\n", $bitfield

makes it come out right.

How can I make bit boolean ops reliable ... or is it a matter of raising my intelligence to stop making foolish mistakes? PS ... This is perl, v5.8.8 built for i686-linux-thread-multi

--
TTTATCGGTCGTTATATAGATGTTTGCA

In reply to bit-wise boolean ops behave differently when observed by TomDLux

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