libcamera: utils: Add set_overlap() function

The new set_overlap() function counts the number of overlapping elements
in the intersection of two sorted ranges defined by their beginning and
ending iterators.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/utils.h

@@ -26,6 +26,25 @@ std::unique_ptr<T> make_unique(Args&&... args)
 
 char *secure_getenv(const char *name);
 
+template<class InputIt1, class InputIt2>
+unsigned int set_overlap(InputIt1 first1, InputIt1 last1,
+			 InputIt2 first2, InputIt2 last2)
+{
+	unsigned int count = 0;
+
+	while (first1 != last1 && first2 != last2) {
+		if (*first1 < *first2) {
+			++first1;
+		} else {
+			if (!(*first2 < *first1))
+				count++;
+			++first2;
+		}
+	}
+
+	return count;
+}
+
 } /* namespace utils */
 
 } /* namespace libcamera */

src/libcamera/utils.cpp

@@ -68,6 +68,18 @@ char *secure_getenv(const char *name)
  * \brief Constructs an object of type T and wraps it in a std::unique_ptr.
  */
 
+/**
+ * \fn libcamera::utils::set_overlap(InputIt1 first1, InputIt1 last1,
+ *				     InputIt2 first2, InputIt2 last2)
+ * \brief Count the number of elements in the intersection of two ranges
+ *
+ * Count the number of elements in the intersection of the sorted ranges [\a
+ * first1, \a last1) and [\a first1, \a last2). Elements are compared using
+ * operator< and the ranges must be sorted with respect to the same.
+ *
+ * \return The number of elements in the intersection of the two ranges
+ */
+
 } /* namespace utils */
 
 } /* namespace libcamera */