kms++util: Add endian.h

Add simple endianness supporting write function, and, for now, only one
shortcut helper, write16le().

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/kms++util/inc/kms++util/endian.h b/kms++util/inc/kms++util/endian.h
new file mode 100644
index 0000000..0f7aecd
--- /dev/null
+++ b/kms++util/inc/kms++util/endian.h
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <type_traits>
+#include <byteswap.h>
+#include <stdint.h>
+
+static_assert((__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) ||
+	      (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__),
+	      "Unable to detect endianness");
+
+enum class endian {
+	little = __ORDER_LITTLE_ENDIAN__,
+	big = __ORDER_BIG_ENDIAN__,
+	native = __BYTE_ORDER__
+};
+
+template<typename T>
+constexpr T byteswap(T value) noexcept
+{
+	static_assert(std::is_integral<T>(), "Type is not integral");
+	static_assert(sizeof(T) == 2 ||
+		      sizeof(T) == 4 ||
+		      sizeof(T) == 8,
+		      "Illegal value size");
+
+	switch (sizeof(T)) {
+		case 2: return bswap_16(value);
+		case 4: return bswap_32(value);
+		case 8: return bswap_64(value);
+	}
+}
+
+template<endian E, typename T>
+static void write_endian(T* dst, T val)
+{
+	if constexpr (E != endian::native)
+		val = byteswap(val);
+
+	*dst = val;
+}
+
+[[maybe_unused]]
+static void write16le(uint16_t* dst, uint16_t val)
+{
+	write_endian<endian::little, uint16_t>(dst, val);
+}