Re: [Qemu-devel] [Qemu-trivial] [PATCH v2] console: Correct computation of bytes per pixel from bits per pixel

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-08-24 13:20, Stefan Hajnoczi wrote:
> On Wed, Aug 22, 2012 at 06:44:08PM +0200, Jan Kiszka wrote:
>> On 2012-08-22 18:29, Stefan Weil wrote:
>>> Am 22.08.2012 17:32, schrieb Jan Kiszka:
>>>> On 2012-08-22 17:19, BALATON Zoltan wrote:
>>>>> Division with round up is the correct way to compute this even if the
>>>>> only case where division with round down gives incorrect result is
>>>>> probably 15 bpp. This case was explicitely patched up in one of these
>>>>> functions but was unhandled in the other. (I'm not sure about setting
>>>>> 16 bpp for the 15bpp case either but I left that there for now.)
>>>>>
>>>>> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
>>>>> ---
>>>>>   console.c |    5 ++---
>>>>>   1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>
>>>>>   v2: Use DIV_ROUND_UP and extended commit message
>>>>>
>>>>> diff --git a/console.c b/console.c
>>>>> index 4525cc7..9df1701 100644
>>>>> --- a/console.c
>>>>> +++ b/console.c
>>>>> @@ -1612,7 +1612,7 @@ PixelFormat
>>>>> qemu_different_endianness_pixelformat(int bpp)
>>>>>       memset(&pf, 0x00, sizeof(PixelFormat));
>>>>>
>>>>>       pf.bits_per_pixel = bpp;
>>>>> -    pf.bytes_per_pixel = bpp / 8;
>>>>> +    pf.bytes_per_pixel = DIV_ROUND_UP(bpp, 8);
>>>>>       pf.depth = bpp == 32 ? 24 : bpp;
>>>>>
>>>>>       switch (bpp) {
>>>>> @@ -1661,13 +1661,12 @@ PixelFormat qemu_default_pixelformat(int bpp)
>>>>>       memset(&pf, 0x00, sizeof(PixelFormat));
>>>>>
>>>>>       pf.bits_per_pixel = bpp;
>>>>> -    pf.bytes_per_pixel = bpp / 8;
>>>>> +    pf.bytes_per_pixel = DIV_ROUND_UP(bpp, 8);
>>>>>       pf.depth = bpp == 32 ? 24 : bpp;
>>>>>
>>>>>       switch (bpp) {
>>>>>           case 15:
>>>>>               pf.bits_per_pixel = 16;
>>>>> -            pf.bytes_per_pixel = 2;
>>>> Removed unintentionally?
>>>>
>>>> Jan
>>>
>>> 15 bpp no longer needs special handling because
>>> the computation above is fixed by the same patch,
>>> so the removal is correct.
>>
>> Ok, actually starting to look at this code: This is apparently a code
>> cleanup, not a bug fix like the subject suggests. No valid input for
>> could have actually triggered the round-up issue. Please declare it as
>> such. Bonus for abort() on the invalid default cases.
> 
> I have updated the commit message to "console: Clean up bytes per pixel
> calculation".

I think there was a v3 on the list, didn't check the details yet, though.

Jan

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