add channel count difference operator.

1 files changed, 25 insertions, 0 deletions

diff --git a/libs/ardour/ardour/chan_count.h b/libs/ardour/ardour/chan_count.h
index ba4a2f17bb..b5699b6743 100644
--- a/libs/ardour/ardour/chan_count.h
+++ b/libs/ardour/ardour/chan_count.h
@@ -147,6 +147,19 @@ public:
 		return ret;
 	}
 
+	/** underflow safe subtraction */
+	ChanCount operator-(const ChanCount& other) const {
+		ChanCount ret;
+		for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
+			if (get(*t) < other.get(*t)) {
+				ret.set(*t, 0);
+			} else {
+				ret.set(*t, get(*t) - other.get(*t));
+			}
+		}
+		return ret;
+	}
+
 	ChanCount operator*(const unsigned int factor) const {
 		ChanCount ret;
 		for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
@@ -155,6 +168,18 @@ public:
 		return ret;
 	}
 
+	/** underflow safe subtraction */
+	ChanCount& operator-=(const ChanCount& other) {
+		for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
+			if (_counts[*t] < other._counts[*t]) {
+				_counts[*t] = 0;
+			} else {
+				_counts[*t] -= other._counts[*t];
+			}
+		}
+		return *this;
+	}
+
 	ChanCount& operator+=(const ChanCount& other) {
 		for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
 			_counts[*t] += other._counts[*t];