A commutative hasher that supports parallel and out-of-order computation - #156
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bb8gh wants to merge 2 commits into
Open
A commutative hasher that supports parallel and out-of-order computation#156bb8gh wants to merge 2 commits into
bb8gh wants to merge 2 commits into
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This is useful in situations where a hash of a large file is needed, but the file is processed non-sequentially (such as blocks being downloaded in parallel). The hash can be built up in any order but still produce the same value for the same input data.
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Copilot review overview
🟡 Changes recommended
Block alignment is not fully enforced, and sequential offsets can overflow on 32-bit targets.
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Review tier: Balanced
Findings: 1
New issues introduced by this change (5)
| Severity | Finding |
|---|---|
 |
crates/commutative_hasher/src/lib.rs — This cumulative offset can overflow on 32-bit targets after a sequential stream exceeds 4 GiB.… |
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crates/commutative_hasher/src/lib.rs — The documented alignment contract is not enforced for data.len(). Any short slice is accepted at… |
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crates/commutative_hasher/src/lib.rs — This 128 MiB hashing test runs in the default suite, despite the repository's explicit `make… |
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crates/commutative_hasher/README.md — The subject is singular, so “always get” should be “always gets.” |
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crates/commutative_hasher/README.md — This Rust example cannot compile: ... is not Rust syntax and no digest value is initialized… |
What changed in this PR
Adds a commutative, block-based Rust hasher supporting parallel and out-of-order processing.
Changes:
- Adds parallel/sequential hashers and digest serialization.
- Adds tests, documentation, and workspace integration.
- Adds optional serde support.
| File | Description |
|---|---|
README.md |
Lists the new crate. |
Makefile |
Tests serde support. |
crates/commutative_hasher/src/lib.rs |
Implements hashers, digests, and tests. |
crates/commutative_hasher/README.md |
Documents usage and behavior. |
crates/commutative_hasher/Cargo.toml |
Defines crate metadata and dependencies. |
Suppressed comments (1)
crates/commutative_hasher/src/lib.rs:542
- This parameterized test hashes and allocates 128 MiB six times in every default test run, and the serde command runs it all again. The repository routes expensive tests through
make test-ignored(Makefile:44-48); please mark this test ignored or use a much smaller multi-block fixture.
#[rstest]
fn test_hash_large_value_sequential(#[values(1, 2, 8, 10, 60, 200)] num_chunks: usize) {
let expected_digest = "ee7338897f6eaf9b4f26b6ec33d3192bca8231485ac70d64fc81128397af0755";
let data = generate_data(1 << 27); // 128 MiB
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This is useful in situations where a hash of a large file is needed, but the file is processed non-sequentially (such as blocks being downloaded in parallel). The hash can be built up in any order but still produce the same value for the same input data.