Re: [PATCH 6/9] drivers/net/wireless/iwlwifi/iwl-4965.c: Correct use of ! and &

Derek M Jones
2008-03-05T12:29:46Z

All,

>>> i think there might be similar patterns: "x & !y", "!x | y", "x | !y" ?
>>>
>> Well, (!x & y) and (!x | y) are probably the two that might have been
>> intended otherwise. (x & !y), (x | !y) are probably ok.
>
> i think the proper intention in the latter cases is (x & ~y) and
> (x | ~y).
>
> My strong bet is that in 99% of the cases they are real bugs and && or
> || was intended.

Developer knowledge of operator precedence and the issue of what
they intended to write are interesting topics. Some experimental
work is described in (binary operators only I'm afraid):

www.knosof.co.uk/cbook/accu06a.pdf
www.knosof.co.uk/cbook/accu07a.pdf

The ACCU 2006 experiment provides evidence that developer knowledge
is proportional to the number of occurrences of a construct in
source code, it also shows a stunningly high percentage of incorrect
answers.

The ACCU 2007 experiment provides evidence that the names of the
operands has a significant impact on operator precedence choice.

I wonder what kind of names are used as the operand of unary
operators?

I would expect the ~ operator to have a bitwise name, but the
! operator might have an arithmetic or bitwise name.

--
Derek M. Jones tel: +44 (0) 1252 520 667
Knowledge Software Ltd mailto:derek@knosof.co.uk
Applications Standards Conformance Testing http://www.knosof.co.uk