[alsa-devel] [PATCH v2] ALSA: usb-audio: Fix max packet size calculation for USB audio

[Ricard Wanderlof]

On Sat, 10 Oct 2015, Ricard Wanderlof wrote:

> > That code was intended to round correctly, but it's obviously wrong
> > because the result is not an integer multiple of the frame size.
> 
> If that is the case we need to do something like
> 
> maxsize = (((freqn + 0xffff) & 0xffff0000) * frame_size) >> 16

Or, much simpler, I realized later:

maxsize = ((freqn + 0xffff) >> 16) * frame_size

i.e. we make the conversion from Q16.16 to integer before multiplying with 
the frame size to automatically get the rounding as intended.

/Ricard
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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