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Date: Thu, 7 Sep 2006 13:38:20 +0200
From: Ed Schouten <ed@fxq.nl>
To: FreeBSD Hackers <freebsd-hackers@freebsd.org>
Message-ID: <20060907113820.GO22564@hoeg.nl>
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X-Mailman-Approved-At: Thu, 07 Sep 2006 12:07:42 +0000
Subject: Oddity in snd_uaudio(4) driver?
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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:

| 	if (speed >=3D UA_SAMP_LO(asf1d) && speed <=3D UA_SAMP_HI(asf1d)) {
| 		ch->sample_rate =3D speed;
| 		return speed;
| 	} else if (speed < UA_SAMP_LO(asf1d)) {
| 		score =3D 0xfff * speed / UA_SAMP_LO(asf1d);
| 		if (score > hiscore) {
| 			bestspeed =3D UA_SAMP_LO(asf1d);
| 			hiscore =3D score;
| 		}
| 	} else if (speed < UA_SAMP_HI(asf1d)) {
| 		score =3D 0xfff * UA_SAMP_HI(asf1d) / speed;
| 		if (score > hiscore) {
| 			bestspeed =3D UA_SAMP_HI(asf1d);
| 			hiscore =3D score;
| 		}
| 	}

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:

| 	if (x >=3D 10 && x <=3D 20) {
| 		...
| 	} else if (x < 10) {
| 		...
| 	} else if (x < 20) {
| 		...
| 	}

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 {'?

Yours,
--=20
 Ed Schouten <ed@fxq.nl>
 WWW: http://g-rave.nl/

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