[program-l] Re: BatteryFlag in system_power_status is negative?
- From: Soronel Haetir <soronel.haetir@xxxxxxxxx>
- To: program-l@xxxxxxxxxxxxx
- Date: Fri, 23 Mar 2012 19:42:17 -0800
I realized after I sent the earlier message that my thinking was a bit
messed up.
An unsigned byte of 255 (hex 0xff) would be interpreted as -1 if
treated as signed (not -128 as I originally said); However an unsigned
byte value 128 (hex 0x80) would be interpreted as -128 if it were
treated as signed. Given that I still think I was on the right track
even if my actual thinking was not entirely correct.
On 3/23/12, Alex Hall <mehgcap@xxxxxxxxx> wrote:
> Great point, I wonder if that's what is happening. The example I found
> uses ctypes data structures to preserve the values, but Python's
> inability to flip the sign using an if statement makes me wonder if it
> is just not reading the byte value properly, as you said. I'll have to
> test this on some other systems and see what happens there.
>
> On 3/23/12, Soronel Haetir <soronel.haetir@xxxxxxxxx> wrote:
>> MSDN says that 255 is "Unknown status - unable to read the battery
>> flag information", 255 and -128 are the same value after taking a
>> possible sign conversion into account.
>>
>> I forget whether python offers unsigned types, especially explicitly
>> sized unsigned types, which is what you would need to directly use the
>> structure in the form it is given (with the values coming out as
>> documented).
>>
>> On 3/23/12, Alex Hall <mehgcap@xxxxxxxxx> wrote:
>>> Hi all,
>>> I am writing a small plugin for nvda to read some system vitals at a
>>> keypress, one of which is battery. I am on a desktop, but many users
>>> have laptops, so the plugin will include battery information if it is
>>> available. The problem, though, is that my BatteryFlag keeps coming
>>> out to -128. Were it 128 I would be happy, since that is the constant
>>> for there being no battery in the system (I have a desktop, so that
>>> works). A negative, though, is not covered anywhere in the document I
>>> found that explains this system_power_structure I am using. I hesitate
>>> to just assume it is the right value but negated, since I am not sure
>>> what will happen on other systems. Has anyone ever heard of this?
>>>
>>> As you may know, nvda plugins are to be written in Python. I found a
>>> forum where someone uses ctypes to grab the system_power_status
>>> structure and convert it to Python, so I am using that code. The
>>> person who used this solution on the forum did not mention any
>>> problems, so I wonder if it is just my system since I am running
>>> Windows via Bootcamp? I really doubt this could be the case, however.
>>>
>>> The strangest part is that I tried to flip the value:
>>> if sps.BatteryFlag<0: sps.BatteryFlag=sps.BatteryFlag*-1
>>> Yet it comes out as -128 whether or not I have that statement in
>>> place. Either Python is not seeing the value (originally a
>>> ctypes.c_byte, if that helps) as negative, or something is going on
>>> that I don't understand. Any help or explanations would be great.
>>> Thanks.
>>>
>>>
>>> --
>>> Have a great day,
>>> Alex (msg sent from GMail website)
>>> mehgcap@xxxxxxxxx; http://www.facebook.com/mehgcap
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>>
>>
>> --
>> Soronel Haetir
>> soronel.haetir@xxxxxxxxx
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>
>
> --
> Have a great day,
> Alex (msg sent from GMail website)
> mehgcap@xxxxxxxxx; http://www.facebook.com/mehgcap
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--
Soronel Haetir
soronel.haetir@xxxxxxxxx
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