Re: [LAD] Possible snd_pcm_hw_params_set_buffer_time_near() gotcha

I guess the problem is that none of the right side variables/constant
is unsigned in:

> unsigned buffer_time = 1000000*period*nperiods/rate;

so regardless of storing it in an unsigned, it overflows before you
try to store it, and so it messes up everything.
Note that you could also prevent this by using the correct constant
10000000U

Victor

On 7 Dec 2009, at 19:22, Mario Lang wrote:

> Hi.
>
> I just happened to stumble about a (what I call) pretty subtle
> bug in typical ALSA PCM code:
>
> root@fzidpc73:/tmp# cat test.c
> #include <stdio.h>
> int main() {
> int period = 1024;
> int nperiods = 3;
> int rate = 96000;
> unsigned buffer_time = 1000000*period*nperiods/rate;
> printf("%d\n", buffer_time);
> }
> root@fzidpc73:/tmp# ./test
> -12739
> root@fzidpc73:/tmp# sed -i -e 's/int rate/unsigned int rate/' test.c
> root@fzidpc73:/tmp# gcc -o test test.c
> root@fzidpc73:/tmp# ./test
> 32000
>
> I.e., don't trust this boilerplate formula blindly.
>
> --
> CYa,
> ⡍⠁⠗⠊⠕
> _______________________________________________
> Linux-audio-dev mailing list
> Linux-audio-dev@lists.linuxaudio.org
> http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev

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Received on Tue Dec 8 00:15:04 2009