intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 21 insertions, 0 deletions

diff --git a/library/cpp/packedtypes/zigzag.h b/library/cpp/packedtypes/zigzag.h
new file mode 100644
index 0000000000..548403f838
--- /dev/null
+++ b/library/cpp/packedtypes/zigzag.h
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <util/generic/typetraits.h>
+
+#include <limits.h>
+
+//! Convert signed values to unsigned. Convenient for further varint encoding.
+//! See https://developers.google.com/protocol-buffers/docs/encoding#types for details.
+
+template <typename TSignedInt>
+inline auto ZigZagEncode(TSignedInt n) -> std::make_unsigned_t<TSignedInt> {
+    static_assert(std::is_signed<TSignedInt>::value && std::is_integral<TSignedInt>::value, "Expected signed integral type.");
+    auto un = static_cast<std::make_unsigned_t<TSignedInt>>(n);
+    return (un << 1) ^ (n >> (CHAR_BIT * sizeof(TSignedInt) - 1));
+}
+
+template <typename TUnsignedInt>
+inline auto ZigZagDecode(TUnsignedInt n) -> std::make_signed_t<TUnsignedInt> {
+    static_assert(std::is_unsigned<TUnsignedInt>::value, "Expected unsigned integral type.");
+    return (n >> 1) ^ -static_cast<std::make_signed_t<TUnsignedInt>>(n & 1);
+}