[alsa-devel] [PATCH v2 04/13] ALSA: dice: cache stream formats at current mode of sampling transmission frequency

[Takashi Sakamoto]

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 at sakamocchi.jp>
>> ---
>>   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.


Thanks

Takashi Sakamoto