allow relative values via +/- prefixes

2 files changed, 50 insertions, 7 deletions

diff --git a/usr.bin/mixerctl/mixerctl.1 b/usr.bin/mixerctl/mixerctl.1
index 7ba18b9abaf..fade672e425 100644
--- a/usr.bin/mixerctl/mixerctl.1
+++ b/usr.bin/mixerctl/mixerctl.1
@@ -1,5 +1,6 @@
-.\" $OpenBSD: mixerctl.1,v 1.4 1998/04/30 13:40:00 provos Exp $
+.\" $OpenBSD: mixerctl.1,v 1.5 1998/05/02 22:28:06 millert Exp $
 .\" $NetBSD: mixerctl.1,v 1.6 1998/04/27 16:55:23 augustss Exp $
+.\"
 .\" Copyright (c) 1997 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
@@ -73,6 +74,13 @@ flag is specified
 .Nm
 attempts to set the specified variables to the given values.
 .Pp
+Values may be specified in either absolute or relative forms.
+The relative form is indicated by a prefix of
+.Dq +
+or
+.Dq -
+to denote an increase or decrease respectively.
+.Pp
 The
 .Fl f
 flag can be used to give an alternative mixer device, the default is
diff --git a/usr.bin/mixerctl/mixerctl.c b/usr.bin/mixerctl/mixerctl.c
index 3ad33b386ec..fbbb034211d 100644
--- a/usr.bin/mixerctl/mixerctl.c
+++ b/usr.bin/mixerctl/mixerctl.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mixerctl.c,v 1.3 1998/04/30 13:40:01 provos Exp $	*/
+/*	$OpenBSD: mixerctl.c,v 1.4 1998/05/02 22:28:07 millert Exp $	*/
 /*	$NetBSD: mixerctl.c,v 1.11 1998/04/27 16:55:23 augustss Exp $	*/
 
 /*
@@ -169,7 +169,7 @@ rdfield(p, q)
 			s = strchr(q, ',');
 			if (s)
 				*s++ = 0;
-			for(i = 0; i < p->infp->un.s.num_mem; i++)
+			for (i = 0; i < p->infp->un.s.num_mem; i++)
 				if (strcmp(p->infp->un.s.member[i].label.name, q) == 0)
 					break;
 			if (i < p->infp->un.s.num_mem) {
@@ -184,17 +184,52 @@ rdfield(p, q)
 	case AUDIO_MIXER_VALUE:
 		if (m->un.value.num_channels == 1) {
 			if (sscanf(q, "%d", &v) == 1) {
-				m->un.value.level[0] = v;
+				switch (*q) {
+				case '+':
+				case '-':
+					m->un.value.level[0] += v;
+					break;
+				default:
+					m->un.value.level[0] = v;
+					break;
+				}
 			} else {
 				warnx("Bad number %s", q);
 				return 0;
 			}
 		} else {
 			if (sscanf(q, "%d,%d", &v0, &v1) == 2) {
-				m->un.value.level[0] = v0;
-				m->un.value.level[1] = v1;
+				switch (*q) {
+				case '+':
+				case '-':
+					m->un.value.level[0] += v0;
+					break;
+				default:
+					m->un.value.level[0] = v0;
+					break;
+				}
+				s = strchr(q, ',') + 1;
+				switch (*s) {
+				case '+':
+				case '-':
+					m->un.value.level[1] += v1;
+					break;
+				default:
+					m->un.value.level[1] = v1;
+					break;
+				}
 			} else if (sscanf(q, "%d", &v) == 1) {
-				m->un.value.level[0] = m->un.value.level[1] = v;
+				switch (*q) {
+				case '+':
+				case '-':
+					m->un.value.level[0] += v;
+					m->un.value.level[1] += v;
+					break;
+				default:
+					m->un.value.level[0] =
+					    m->un.value.level[1] = v;
+					break;
+				}
 			} else {
 				warnx("Bad numbers %s", q);
 				return 0;