zerovec

Zero-copy vector abstractions over byte arrays.

zerovec enable vectors of multibyte types to be backed by a byte array, abstracting away issues including memory alignment and endianness.

This crate has four main types:

• ZeroVec<T> for fixed-width types like u32
• VarZeroVec<T> for variable-width types like str
• ZeroMap<K, V> to map from K to V
• ZeroMap2d<K0, K1, V> to map from the pair (K0, K1) to V

The first two are intended as drop-in replacements for Vec<T> in Serde structs serialized with a format supporting a borrowed byte buffer, like Bincode. The third and fourth are intended as a replacement for HashMap or LiteMap.

Clients upgrading to zerovec benefit from zero heap allocations when deserializing read-only data.

This crate has two optional features: serde and yoke. serde allows serializing and deserializing zerovec's abstractions via serde, and yoke enables implementations of Yokeable from the yoke crate.

Performance

zerovec is designed for fast deserialization from byte buffers with zero memory allocations while minimizing performance regressions for common vector operations.

Benchmark results on x86_64:

| Operation | Vec<T> | zerovec | |---|---|---| | Deserialize vec of 100 u32 | 233.18 ns | 14.120 ns | | Compute sum of vec of 100 u32 (read every element) | 8.7472 ns | 10.775 ns | | Binary search vec of 1000 u32 50 times | 442.80 ns | 472.51 ns | | Deserialize vec of 100 strings | 7.3740 μs* | 1.4495 μs | | Count chars in vec of 100 strings (read every element) | 747.50 ns | 955.28 ns | | Binary search vec of 500 strings 10 times | 466.09 ns | 790.33 ns |

* This result is reported for Vec<String>. However, Serde also supports deserializing to Vec<&str>; this gives 1.8420 μs, much faster than Vec<String> but a bit slower than zerovec.

| Operation | HashMap<K,V> | LiteMap<K,V> | ZeroMap<K,V> | |---|---|---|---| | Deserialize a small map | 2.72 μs | 1.28 μs | 480 ns | | Deserialize a large map | 50.5 ms | 18.3 ms | 3.74 ms | | Look up from a small deserialized map | 49 ns | 42 ns | 54 ns | | Look up from a large deserialized map | 51 ns | 155 ns | 213 ns |

Small = 16 elements, large = 131,072 elements. Maps contain <String, String>.

The benches used to generate the above table can be found in the benches directory in the project repository. zeromap benches are named by convention, e.g. zeromap/deserialize/small, zeromap/lookup/large. The type is appended for baseline comparisons, e.g. zeromap/lookup/small/hashmap.

Features

• serde: enables Serde Serialize/Deserialize impls for ZeroVec and VarZeroVec.

Examples

Serialize and deserialize a struct with ZeroVec and VarZeroVec with Bincode:

```rust use zerovec::{ZeroVec, VarZeroVec};

// This example requires the "serde" feature

[derive(serde::Serialize, serde::Deserialize)]

pub struct DataStruct<'data> { #[serde(borrow)] nums: ZeroVec<'data, u32>, #[serde(borrow)] strs: VarZeroVec<'data, str>, }

let data = DataStruct { nums: ZeroVec::fromslice(&[211, 281, 421, 461]), strs: VarZeroVec::from(&["hello", "world"]), }; let bincodebytes = bincode::serialize(&data) .expect("Serialization should be successful"); asserteq!(54, bincodebytes.len());

let deserialized: DataStruct = bincode::deserialize(&bincodebytes) .expect("Deserialization should be successful"); asserteq!(Some(211), deserialized.nums.first()); asserteq!(Some("world"), deserialized.strs.get(1)); assert!(matches!(deserialized.nums, ZeroVec::Borrowed())); ```

More Information

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