Re: [Qemu-devel] [PATCH 1/5] ide: Prohibit RESET on IDE drives

[Laszlo Ersek <lersek@redhat.com>]

On 01/19/16 18:04, John Snow wrote:
> 
> 
> On 01/19/2016 06:48 AM, Paolo Bonzini wrote:
>>
>>
>> On 19/01/2016 05:51, John Snow wrote:
>>> +    /* Only RESET is allowed to an ATAPI device while BSY and/or DRQ are set. */
>>> +    if (s->status & (BUSY_STAT|DRQ_STAT)) {
>>> +        if (!(val == WIN_DEVICE_RESET) && (s->drive_kind == IDE_CD)) {
>>
>> I was going to complain about Pascal-ish parentheses, but actually I
>> think there is a bug here; the expression just looks weird.
>>
>> Did you mean
>>
>> 	if (!(val == WIN_DEVICE_RESET && s->drive_kind == IDE_CD))
>>
>> or equivalently applying de Morgan's law:
>>
>> 	if (s->drive_kind != IDE_CD || val != WIN_DEVICE_RESET)
>>
>> ?
>>
>> Paolo
>>
>>> +            return;
>>
> 
> ugh, yes, I typo'd. Thank you.
> 
> If you're still up, which do you find more readable?
> The (!(A && B)) form or the (!A || !B) form?

You didn't ask me, but that's no problem for me. :)

The logical negation operator "!" has much-much stronger binding than
the logical "and" and logical "or" ones. If you use the first form,

  !(A && B)

it works, but spacetime will curl every time someone sees those
parentheses overriding the nice n' tight binding of "!".

So, for me, only the second form *exists* -- for me, the operand of the
logical negation operator must always be as "indivisible" an expression
as possible :)

So,

  (!A || !B)

without a doubt.

Thanks
Laszlo