Date: Thu, 07 Sep 2006 14:27:44 +0200 From: Alexander Leidinger <Alexander@Leidinger.net> To: FreeBSD Hackers <freebsd-hackers@FreeBSD.org>, Ed Schouten <ed@fxq.nl> Cc: multimedia@FreeBSD.org Subject: Re: Oddity in snd_uaudio(4) driver? Message-ID: <20060907142744.aazrsemxkwcok40w@webmail.leidinger.net> In-Reply-To: <20060907113820.GO22564@hoeg.nl> References: <20060907113820.GO22564@hoeg.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
Quoting Ed Schouten <ed@fxq.nl> (from Thu, 7 Sep 2006 13:38:20 +0200):
CCing multimedia@, where all "the cool sound guys hang out"...
> Hello,
>
> I was just looking through FreeBSD's snd_uaudio(4) driver, because I'm
> thinking of patching it to support Xbox 360 headsets as well. I was
> looking at the code to set the sample rate in
> /sys/dev/sound/usb/uaudio.c. In that file there is the following code
> near line 4100:
>
> | =09if (speed >=3D UA_SAMP_LO(asf1d) && speed <=3D UA_SAMP_HI(asf1d)) {
> | =09=09ch->sample_rate =3D speed;
> | =09=09return speed;
> | =09} else if (speed < UA_SAMP_LO(asf1d)) {
> | =09=09score =3D 0xfff * speed / UA_SAMP_LO(asf1d);
> | =09=09if (score > hiscore) {
> | =09=09=09bestspeed =3D UA_SAMP_LO(asf1d);
> | =09=09=09hiscore =3D score;
> | =09=09}
> | =09} else if (speed < UA_SAMP_HI(asf1d)) {
> | =09=09score =3D 0xfff * UA_SAMP_HI(asf1d) / speed;
> | =09=09if (score > hiscore) {
> | =09=09=09bestspeed =3D UA_SAMP_HI(asf1d);
> | =09=09=09hiscore =3D score;
> | =09=09}
> | =09}
>
> If we would rewrite this code to something more basic, let's say we
> rename 'speed' to 'x' and the UA_SAMP_ macros to some predefined
> variables:
>
> | =09if (x >=3D 10 && x <=3D 20) {
> | =09=09...
> | =09} else if (x < 10) {
> | =09=09...
> | =09} else if (x < 20) {
> | =09=09...
> | =09}
>
> Wouldn't that mean that the last portion of the code is never reached?
> Looking at the code, it looks like some range check, making sure the
> sample rate remains inside a certain range. Wouldn't it be enough to
> remove the entire third if-statement, using a normal '} else {'?
Just by looking at the code you pasted, I assume the last part is a =20
typo in the uaudio code and should be a '>' instead of a '<': "if it =20
is outside the range, use the end of the range as a good candidate."
Bye,
Alexander.
--=20
The most delightful day after the one on which you buy a cottage in
the country is the one on which you resell it.
=09=09-- J. Brecheux
http://www.Leidinger.net Alexander @ Leidinger.net: PGP ID =3D B0063FE7
http://www.FreeBSD.org netchild @ FreeBSD.org : PGP ID =3D 72077137
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20060907142744.aazrsemxkwcok40w>