[alsa-devel] [PATCH - Intervals v2 1/1] interval: Interpret (x x+1] correctly and return x+1

[Timo Wischer]

On 10/18/18 16:45, Takashi Sakamoto wrote:
> Hi,
>
> On Thu, 18 Oct 2018, Timo Wischer wrote:
>> The reason for this fix was an issue where an interval of (x x+1] is 
>> interpreted as not a single value.
>> Before the change in snd_interval_single() the following intervals 
>> were interpreted as a single value:
>>
>> * (x x) -> required for rounding issues e.g. 32ms * 22,05 kHz = 705,6
>>   frames => (705 706)
>> * (x x]
>> * [x x)
>> * [x x]
>> * (x x+1)
>> * [x x+1)
>>
>> With this change (x x+1] will also be interpreted as a single value 
>> (which looks reasonable for me).
>> But the interval [x x+1] is still not interpreted as a single value 
>> (which also sounds right for me)
>>
>> Before the change in snd_interval_value() for all intervals x was 
>> returned.
>> With this change only in case (x x+1] x+1 will be returned. All other 
>> intervals are not changed.
>>
>> Therefore this is a minimal change which solves issues. I have 
>> already at least two use cases which
>> are failing without this fix. (Somehow simple use cases with 
>> rate->dmix->hw where the hw truncates
>> the default period_time of 125ms and fails with EINVAL on 
>> snd_pcm_set_period_near()).
>> Therefore I would expect that these issues will be seen soon by other 
>> users.
>>
>> If there is a use case which breaks in future due to the right 
>> interpretation of (x x+1] I think we should try
>> to find the root cause why this (x x+1] interval has to be 
>> interpreted wrongly to get the use case to work.
>
> 'struct snd_interval' has 'integer' flag. When this flag is off,
> '(x, x + 1]' brings no single unique value. The inline function
> 'snd_interval_single()' should handle this case correctly.
Okay. Thanks for the hint. I think than I does not yet got the meaning 
of the integer flag correctly. My expectation was that the interval is 
interpreted as a real number interval in case integer is not set and 
interpreted as a natural number interval. Therefore in case of integer 
is not set the interval includes all real numbers which are >x and <=x+1 
e.g. the interval (1 2] includes 1.89 and 2.

In case of integer flag is set I would expect the same rule >x and <=x+1 
e.g. (1 2] only 2 is included because this is the only natural number 
which is >1 and <=2.

Please correct me if I am wrong.

>
>
> Thanks
>
> Takashi Sakamoto (@airport)