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

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

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.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux