util.bitops: Library to find appropriate bitwise library (closes #1395)

util/bitcompat.lua

@@ -0,0 +1,32 @@
+-- Compatibility layer for bitwise operations
+
+-- First try the bit32 lib
+-- Lua 5.3 has it with compat enabled
+-- Lua 5.2 has it by default
+if _G.bit32 then
+	return _G.bit32;
+else
+	-- Lua 5.1 may have it as a standalone module that can be installed
+	local ok, bitop = pcall(require, "bit32")
+	if ok then
+		return bitop;
+	end
+end
+
+do
+	-- Lua 5.3 and 5.4 would be able to use native infix operators
+	local ok, bitop = pcall(require, "util.bit53")
+	if ok then
+		return bitop;
+	end
+end
+
+do
+	-- Lastly, try the LuaJIT bitop library
+	local ok, bitop = pcall(require, "bit")
+	if ok then
+		return bitop;
+	end
+end
+
+error "No bit module found. See https://prosody.im/doc/depends#bitop";