Set:

$flags |= 1 << $bit_num;
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Clear:

$flags &= ~( 1 << $bit_num );
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Toggle:

$flags ^= 1 << $bit_num;
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Read (returns a true value or a false value):

$flags & ( 1 << $bit_num )
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It looks like you have constants that are already of the form 1 << $bit_num, so

$stats &= ~downLoading;   # No longer downloading.
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