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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2021-12-06 16:21:19 +0200
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2021-12-07 19:09:31 +0200
commitf413f944d789911c9ded831ac45a7674c129ceba (patch)
treec09d9d0e96e9e504d3a35c7d02e5c31d33908b1b
parent72679c682eb0b9f03948f258a26f78c037d33c48 (diff)
libcamera: base: utils: Add abs_diff() utility function
The abs_diff() function computes the absolute difference of two elements. This may seem trivial at first, but can lead to unexpected results when operating on unsigned operands. A common implementation of the absolute difference of two unsigned int (used through the libcamera code base) is std::abs(static_cast<int>(a - b)) but doesn't return the expected result when either a or b is larger than UINT_MAX / 2 due to overflows. The abs_diff() function offers a safe alternative. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
-rw-r--r--include/libcamera/base/utils.h9
-rw-r--r--src/libcamera/base/utils.cpp17
2 files changed, 26 insertions, 0 deletions
diff --git a/include/libcamera/base/utils.h b/include/libcamera/base/utils.h
index 3a803176..9ab18101 100644
--- a/include/libcamera/base/utils.h
+++ b/include/libcamera/base/utils.h
@@ -346,6 +346,15 @@ public:
}
};
+template<typename T>
+decltype(auto) abs_diff(const T &a, const T &b)
+{
+ if (a < b)
+ return b - a;
+ else
+ return a - b;
+}
+
} /* namespace utils */
#ifndef __DOXYGEN__
diff --git a/src/libcamera/base/utils.cpp b/src/libcamera/base/utils.cpp
index 45b92b67..8cf8a5b2 100644
--- a/src/libcamera/base/utils.cpp
+++ b/src/libcamera/base/utils.cpp
@@ -437,6 +437,23 @@ std::string toAscii(const std::string &str)
* \return True if \a Duration is a non-zero time value, False otherwise
*/
+/**
+ * \fn abs_diff(const T& a, const T& b)
+ * \brief Calculates the absolute value of the difference between two elements
+ * \param[in] a The first element
+ * \param[in] b The second element
+ *
+ * This function calculates the absolute value of the difference between two
+ * elements of the same type, in such a way that a negative value will never
+ * occur during the calculation.
+ *
+ * This is inspired by the std::abs_diff() candidate proposed in N4318
+ * (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4318.pdf).
+ *
+ * \return The absolute value of the difference of the two parameters \a a and
+ * \a b
+ */
+
} /* namespace utils */
#ifndef __DOXYGEN__