libcamera: utils: Add hex stream output helper

Add a utils::hex() function that simplifies writing hexadecimal values
to an ostream. The function handles the '0x' prefix, the field width and
the fill character automatically. Use it through the libcamera code
base, and add a test.

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

1 files changed, 39 insertions, 0 deletions

diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
index 928db254..d632f6e6 100644
--- a/src/libcamera/utils.cpp
+++ b/src/libcamera/utils.cpp
@@ -143,6 +143,45 @@ std::string time_point_to_string(const time_point &time)
 	return ossTimestamp.str();
 }
 
+std::basic_ostream<char, std::char_traits<char>> &
+operator<<(std::basic_ostream<char, std::char_traits<char>> &stream, const _hex &h)
+{
+	stream << "0x";
+
+	std::ostream::fmtflags flags = stream.setf(std::ios_base::hex,
+						   std::ios_base::basefield);
+	std::streamsize width = stream.width(h.w);
+	char fill = stream.fill('0');
+
+	stream << h.v;
+
+	stream.flags(flags);
+	stream.width(width);
+	stream.fill(fill);
+
+	return stream;
+}
+
+/**
+ * \fn hex(T value, unsigned int width)
+ * \brief Write an hexadecimal value to an output string
+ * \param value The value
+ * \param width The width
+ *
+ * Return an object of unspecified type such that, if \a os is the name of an
+ * output stream of type std::ostream, and T is an integer type, then the
+ * expression
+ *
+ * \code{.cpp}
+ * os << utils::hex(value)
+ * \endcode
+ *
+ * will output the \a value to the stream in hexadecimal form with the base
+ * prefix and the filling character set to '0'. The field width is set to \a
+ * width if specified to a non-zero value, or to the native width of type T
+ * otherwise. The \a os stream configuration is not modified.
+ */
+
 } /* namespace utils */
 
 } /* namespace libcamera */