protobuf/
zigzag.rs

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1// ZigZag endoging used for efficient transfer of signed integers
2// https://developers.google.com/protocol-buffers/docs/encoding#types
3
4use crate::rt::compute_raw_varint32_size;
5use crate::rt::compute_raw_varint64_size;
6
7pub(crate) fn decode_zig_zag_32(n: u32) -> i32 {
8    ((n >> 1) as i32) ^ (-((n & 1) as i32))
9}
10
11pub(crate) fn decode_zig_zag_64(n: u64) -> i64 {
12    ((n >> 1) as i64) ^ (-((n & 1) as i64))
13}
14
15pub(crate) fn encode_zig_zag_32(n: i32) -> u32 {
16    ((n << 1) ^ (n >> 31)) as u32
17}
18
19pub(crate) fn encode_zig_zag_64(n: i64) -> u64 {
20    ((n << 1) ^ (n >> 63)) as u64
21}
22
23/// Helper trait implemented by integer types which could be encoded as zigzag varint.
24pub(crate) trait ProtobufVarintZigzag {
25    /// Size of self when encoded as zigzag varint.
26    fn len_varint_zigzag(&self) -> u64;
27}
28
29impl ProtobufVarintZigzag for i64 {
30    fn len_varint_zigzag(&self) -> u64 {
31        compute_raw_varint64_size(encode_zig_zag_64(*self))
32    }
33}
34
35impl ProtobufVarintZigzag for i32 {
36    fn len_varint_zigzag(&self) -> u64 {
37        compute_raw_varint32_size(encode_zig_zag_32(*self))
38    }
39}
40
41#[cfg(test)]
42mod test {
43
44    use super::decode_zig_zag_32;
45    use super::decode_zig_zag_64;
46    use super::encode_zig_zag_32;
47    use super::encode_zig_zag_64;
48
49    #[test]
50    fn test_zig_zag() {
51        fn test_zig_zag_pair_64(decoded: i64, encoded: u64) {
52            assert_eq!(decoded, decode_zig_zag_64(encoded));
53            assert_eq!(encoded, encode_zig_zag_64(decoded));
54        }
55
56        fn test_zig_zag_pair(decoded: i32, encoded: u32) {
57            assert_eq!(decoded, decode_zig_zag_32(encoded));
58            assert_eq!(encoded, encode_zig_zag_32(decoded));
59            test_zig_zag_pair_64(decoded as i64, encoded as u64);
60        }
61
62        test_zig_zag_pair(0, 0);
63        test_zig_zag_pair(-1, 1);
64        test_zig_zag_pair(1, 2);
65        test_zig_zag_pair(-2, 3);
66        test_zig_zag_pair(2147483647, 4294967294);
67        test_zig_zag_pair(-2147483648, 4294967295);
68        test_zig_zag_pair_64(9223372036854775807, 18446744073709551614);
69        test_zig_zag_pair_64(-9223372036854775808, 18446744073709551615);
70    }
71}
protobuf/zigzag.rs

protobuf/
zigzag.rs
