mirror of
https://github.com/clockworklabs/SpacetimeDB.git
synced 2026-05-16 04:37:55 -04:00
Kim Altintop
1d316d991e
Defines the canonical commitlog payload, and how to encode / decode it. Also exposes folds alongside iterators, which allows the common case of replaying the commitlog onto a database to be further optimized (the `Txdata` does not have to be constructed in this case). This optimization is, however, left for a future patch.
66 lines
1.9 KiB
Rust
66 lines
1.9 KiB
Rust
//! Varint encoding and decoding functions.
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//!
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//! We use Protobuf's [Base-128 varint] encoding.
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//!
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//! Unsigned integers are split into 7-bit chunks, with the least significant
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//! chunk first.
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//! Each chunk is placed in the low 7 bits of a byte.
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//! Non-terminal bytes have the high bit set.
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//! The final byte in an integer has the high bit zeroed.
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//!
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//! NOTE: In the current commitlog format, varints are expected to fit into one
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//! byte most of the time. Hence, the implementation below is not particularly
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//! optimized for larger integers.
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//! Should this change in the future, various crates are available for
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//! consideration, including [varint-simd] which provides hardware acceleration
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//! on certain architectures.
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//!
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//! [Base-128 varint]: https://protobuf.dev/programming-guides/encoding/#varints
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//! [varint-simd]: https://crates.io/crates/varint-simd
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use spacetimedb_sats::buffer::{BufReader, BufWriter, DecodeError};
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#[inline]
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pub fn encode_varint(mut value: usize, out: &mut impl BufWriter) {
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loop {
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if value < 0x80 {
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out.put_u8(value as u8);
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break;
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} else {
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out.put_u8(((value & 0x7f) | 0x80) as u8);
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value >>= 7;
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}
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}
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}
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#[inline]
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pub fn decode_varint<'a>(reader: &mut impl BufReader<'a>) -> Result<usize, DecodeError> {
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let mut result = 0;
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let mut shift = 0;
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loop {
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let byte = reader.get_u8()?;
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if (byte & 0x80) == 0 {
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result |= (byte as usize) << shift;
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return Ok(result);
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} else {
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result |= ((byte & 0x7F) as usize) << shift;
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}
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shift += 7;
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use proptest::prelude::*;
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proptest! {
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#[test]
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fn varint_roundtrip(val in any::<usize>()) {
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let mut buf = Vec::new();
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encode_varint(val, &mut buf);
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assert_eq!(val, decode_varint(&mut buf.as_slice()).unwrap());
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}
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}
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}
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