On Tue, 01 May 2018 05:02:09 +0200,
Takashi Sakamoto wrote:
>
> Hi,
>
> On May 1 2018 00:10, Takashi Iwai wrote:
> > On Sun, 29 Apr 2018 08:50:23 +0200,
> > Takashi Sakamoto wrote:
> >>
> >> In former commits, proxy structure get members for cache of stream
> >> formats. This commit fills the cache with stream formats at current mode
> >> of sampling transmission frequency.
> >>
> >> Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
> >> ---
> >> sound/firewire/dice/dice-stream.c | 76 +++++++++++++++++++++++++++++++++++++++
> >> sound/firewire/dice/dice.c | 4 +++
> >> sound/firewire/dice/dice.h | 3 ++
> >> 3 files changed, 83 insertions(+)
> >>
> >> diff --git a/sound/firewire/dice/dice-stream.c b/sound/firewire/dice/dice-stream.c
> >> index 928a255bfc35..2a9f0cd994a5 100644
> >> --- a/sound/firewire/dice/dice-stream.c
> >> +++ b/sound/firewire/dice/dice-stream.c
> >> @@ -30,6 +30,24 @@ const unsigned int snd_dice_rates[SND_DICE_RATES_COUNT] = {
> >> [6] = 192000,
> >> };
> >> +int snd_dice_stream_get_rate_mode(struct snd_dice *dice,
> >> unsigned int rate,
> >> + unsigned int *mode)
> >> +{
> >> + int i;
> >> +
> >> + for (i = 0; i < ARRAY_SIZE(snd_dice_rates); i++) {
> >> + if (!(dice->clock_caps & BIT(i)))
> >> + continue;
> >> + if (snd_dice_rates[i] != rate)
> >> + continue;
> >> +
> >> + *mode = (i - 1) / 2;
> >
> > What if i=0? It'll be a negative value?
>
> Yes. But division by 2 to -1 results in 0 because in C language
> specification 'truncate toward zero'[1] is applied to discard
> fractional part. Then, the result is assigned to value of 'unsigned int'
> type. As a result:
>
> 0: 32000/44100/48000
> 1: 88200/96000
> 2: 176400/192000
>
> This is what I expect.
>
> [1] footnote for '6.5.5 Multiplicative operators' clause in ISO/IEC 9899.
This is too tricky. The result would change dramatically when i were
declared as unsigned.
And I can think of someone trying to change it unsigned because of the
comparison against ARRAY_SIZE() (we've got gcc warnings for that in
the past).
Please make either it more robust or put a proper comment.
thanks,
Takashi
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