utils: Add unary negation operation to Duration

In the near future we will add a SyncAdjustment control for adjusting
the frame duration via the sync algorithm. This control needs to be able
to take on a negative value, since the frame duration can be shortened
in addition to being extended. While the control is an int, it would be
convenient to be able to clamp it to frame duration limits, which are
usually handled as utils::Duration values internally. To allow this
using utils::Duration, add a unary negation operation to
utils::Duration. Also add a test for the operator.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/base/utils.h

@@ -394,6 +394,11 @@ public:
 		return c.count();
 	}
 
+	constexpr Duration operator-() const
+	{
+		return BaseDuration::operator-();
+	}
+
 	explicit constexpr operator bool() const
 	{
 		return *this != BaseDuration::zero();

src/libcamera/base/utils.cpp

@@ -425,6 +425,12 @@ std::string toAscii(const std::string &str)
  * \return The tick count of the Duration expressed in \a Period
  */
 
+/**
+ * \fn Duration::operator-()
+ * \brief Negation operator to negate a \a Duration
+ * \return The duration, with the number of ticks negated
+ */
+
 /**
  * \fn Duration::operator bool()
  * \brief Boolean operator to test if a \a Duration holds a non-zero time value

test/utils.cpp

@@ -167,6 +167,12 @@ protected:
 			return TestFail;
 		}
 
+		exposure = 100ms;
+		if ((-exposure).get<std::milli>() != -100) {
+			cerr << "utils::Duration failed negation" << endl;
+			return TestFail;
+		}
+
 		return TestPass;
 	}