On 05/02/2015 07:23 PM, Prashant Laddha wrote:
> The intermediate calculation in the expression for hblank can exceed
> 32 bit signed range. This overflow can lead to negative values for
> hblank. Typecasting intermediate variable to higher precision.
>
> Cc: Hans Verkuil
> Cc: Martin Bugge
> Signed-off-by: Prashant Laddha
> ---
> drivers/media/v4l2-core/v4l2-dv-timings.c | 16
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-dv-timings.c
> b/drivers/media/v4l2-core/v4l2-dv-timings.c
> index 86e11d1..9d27f05 100644
> --- a/drivers/media/v4l2-core/v4l2-dv-timings.c
> +++ b/drivers/media/v4l2-core/v4l2-dv-timings.c
> @@ -573,15 +573,15 @@ bool v4l2_detect_gtf(unsigned frame_height,
>
> /* Horizontal */
> if (default_gtf)
> - h_blank = ((image_width * GTF_D_C_PRIME * hfreq) -
> - (image_width * GTF_D_M_PRIME * 1000) +
> - (hfreq * (100 - GTF_D_C_PRIME) + GTF_D_M_PRIME * 1000)
> / 2) /
> - (hfreq * (100 - GTF_D_C_PRIME) + GTF_D_M_PRIME * 1000);
> + h_blank = ((image_width * GTF_D_C_PRIME * (long long)hfreq) -
> + ((long long)image_width * GTF_D_M_PRIME * 1000) +
> + ((long long)hfreq * (100 - GTF_D_C_PRIME) +
> GTF_D_M_PRIME * 1000) / 2) /
> + ((long long)hfreq * (100 - GTF_D_C_PRIME) +
> GTF_D_M_PRIME * 1000);
This will not work on systems that cannot divide 64 bit numbers. Use the do_div
function for this. It's a common mistake to make when developing on Intel CPUs.
Been there, done that :-) Multiple times, in fact...
And I think it will help a lot if some additional variables are introduced since
this calculation is getting complex.
Also replace "/ 2" by ">> 1". That will guarantee that you do not need do_div
for
that. Probably unnecessary since I would expect gcc to be smart enough to
replace
/ 2 by >> 1 anyway, but it doesn't hurt.
Regards,
Hans
> else
> - h_blank = ((image_width * GTF_S_C_PRIME * hfreq) -
> - (image_width * GTF_S_M_PRIME * 1000) +
> - (hfreq * (100 - GTF_S_C_PRIME) + GTF_S_M_PRIME * 1000)
> / 2) /
> - (hfreq * (100 - GTF_S_C_PRIME) + GTF_S_M_PRIME * 1000);
> + h_blank = ((image_width * GTF_S_C_PRIME * (long long)hfreq) -
> + ((long long)image_width * GTF_S_M_PRIME * 1000) +
> + ((long long)hfreq * (100 - GTF_S_C_PRIME) +
> GTF_S_M_PRIME * 1000) / 2) /
> + ((long long)hfreq * (100 - GTF_S_C_PRIME) +
> GTF_S_M_PRIME * 1000);
>
> h_blank = ((h_blank + GTF_CELL_GRAN) / (2 * GTF_CELL_GRAN)) *
> (2 * GTF_CELL_GRAN);
>
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