diff --git a/autotest/SignificantBits/SignificantBits.cpp b/autotest/SignificantBits/SignificantBits.cpp
new file mode 100644
index 000000000..9199edcb0
--- /dev/null
+++ b/autotest/SignificantBits/SignificantBits.cpp
@@ -0,0 +1,21 @@
+#include <Core/Core.h>
+
+using namespace Upp;
+
+CONSOLE_APP_MAIN
+{
+	StdLogSetup(LOG_COUT|LOG_FILE);
+
+	for(int i = -1; i < 64; i++) {
+		uint64 v = i >= 0 ? (uint64)1 << i : 0;
+		LOG("===============");
+		DUMPHEX(v);
+		DUMP(SignificantBits64(v));
+		DUMP(SignificantBits(v));
+		if(i < 32)
+			ASSERT(SignificantBits((dword)v) == i + 1);
+		ASSERT(SignificantBits64(v) == i + 1);
+	}
+	
+	LOG("================= OK");
+}
diff --git a/autotest/SignificantBits/SignificantBits.upp b/autotest/SignificantBits/SignificantBits.upp
new file mode 100644
index 000000000..887ea4bea
--- /dev/null
+++ b/autotest/SignificantBits/SignificantBits.upp
@@ -0,0 +1,9 @@
+uses
+	Core;
+
+file
+	SignificantBits.cpp;
+
+mainconfig
+	"" = "";
+