1 files changed, 50 insertions, 0 deletions
diff --git a/src/zigzag.rs b/src/zigzag.rs
new file mode 100644
index 0000000..4c7d27d
--- /dev/null
+++ b/src/zigzag.rs
@@ -0,0 +1,50 @@
+// ZigZag endoging used for efficient transfer of signed integers
+// https://developers.google.com/protocol-buffers/docs/encoding#types
+
+pub fn decode_zig_zag_32(n: u32) -> i32 {
+    ((n >> 1) as i32) ^ (-((n & 1) as i32))
+}
+
+pub fn decode_zig_zag_64(n: u64) -> i64 {
+    ((n >> 1) as i64) ^ (-((n & 1) as i64))
+}
+
+pub fn encode_zig_zag_32(n: i32) -> u32 {
+    ((n << 1) ^ (n >> 31)) as u32
+}
+
+pub fn encode_zig_zag_64(n: i64) -> u64 {
+    ((n << 1) ^ (n >> 63)) as u64
+}
+
+#[cfg(test)]
+mod test {
+
+    use super::decode_zig_zag_32;
+    use super::decode_zig_zag_64;
+    use super::encode_zig_zag_32;
+    use super::encode_zig_zag_64;
+
+    #[test]
+    fn test_zig_zag() {
+        fn test_zig_zag_pair_64(decoded: i64, encoded: u64) {
+            assert_eq!(decoded, decode_zig_zag_64(encoded));
+            assert_eq!(encoded, encode_zig_zag_64(decoded));
+        }
+
+        fn test_zig_zag_pair(decoded: i32, encoded: u32) {
+            assert_eq!(decoded, decode_zig_zag_32(encoded));
+            assert_eq!(encoded, encode_zig_zag_32(decoded));
+            test_zig_zag_pair_64(decoded as i64, encoded as u64);
+        }
+
+        test_zig_zag_pair(0, 0);
+        test_zig_zag_pair(-1, 1);
+        test_zig_zag_pair(1, 2);
+        test_zig_zag_pair(-2, 3);
+        test_zig_zag_pair(2147483647, 4294967294);
+        test_zig_zag_pair(-2147483648, 4294967295);
+        test_zig_zag_pair_64(9223372036854775807, 18446744073709551614);
+        test_zig_zag_pair_64(-9223372036854775808, 18446744073709551615);
+    }
+}