kern/65485: sb16 mixer: uneven mapping from % volume to absolute volume

[Andriy Gapon]

>Number:         65485
>Category:       kern
>Synopsis:       sb16 mixer: uneven mapping from % volume to absolute volume
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Apr 13 04:50:13 PDT 2004
>Closed-Date:
>Last-Modified:
>Originator:     Andriy Gapon
>Release:        FreeBSD 5.2.1-RELEASE-p4 i386
>Organization:
>Environment:
System: FreeBSD x.x.x.x 5.2.1-RELEASE-p4 FreeBSD 5.2.1-RELEASE-p4 #16: Fri Apr 2 20:05:58 EEST 2004 avg i386
any i386 FreeBSD 4.x, 5.x with SB16


	
>Description:
	current function for mapping userland relative volume levels (0-100) to device volume levels looks like this:

left = (left * max) / 100;

this is probably good enough for main or pcm volume where max=31, but is suboptimal for ogain, where max=3, because 0-100 range is virtually split into only 3 subranges instead of possible 4: 
00-33 => 0
34-66 => 1
67-99 => 2
100 => 3

IMHO, something like the following fomula should do better:
abs = [(max+1)*rel/max]*max/100
[] stands fo integer part
>How-To-Repeat:
	
try to regulate ogain and you will see /hear :-)/ that 0-100 range is actually split into 3 subranges and maximum is reached only when volume==100%
>Fix:

	

--- sb16.c.patch begins here ---
--- sb16.c.orig	Tue Apr 13 14:09:46 2004
+++ sb16.c	Tue Apr 13 14:10:03 2004
@@ -326,6 +326,12 @@
 }
 
 static int
+rel2abs_volume(int x, int max)
+{
+	return ((((max + 1) * x) / max) * max) / 100;
+}
+
+static int
 sb16mix_set(struct snd_mixer *m, unsigned dev, unsigned left, unsigned right)
 {
     	struct sb_info *sb = mix_getdevinfo(m);
@@ -335,8 +341,8 @@
 	e = &sb16_mixtab[dev];
 	max = (1 << e->bits) - 1;
 
-	left = (left * max) / 100;
-	right = (right * max) / 100;
+	left = rel2abs_volume(left, max);
+	right = rel2abs_volume(right, max);
 
 	sb_setmixer(sb, e->reg, left << e->ofs);
 	if (e->stereo)
--- sb16.c.patch ends here ---

>Release-Note:
>Audit-Trail:
>Unformatted: