Elamur Groupantsmlab-rng-stream
The groupant beside mlab/src/rng.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.
Facts
Implementation material. A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.
Components
| component | label | where |
|---|---|---|
| approximant | partial | approximant |
| ast | partial | ../syntax.json |
| cost | symbolic source derived | invariant |
| descriptant | present | descriptant |
| invariant | partial | invariant |
| tests | partial bounded parent evidence | tests |
Obernants
The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.
| id | type | label | where |
|---|---|---|---|
behavior_complement | behavior_complement | partial source derived model | behavior_complement |
reverse_reconstruction | reverse_reconstruction | partial source derived model | reverse_reconstruction |
uniform_grid | uniform_grid | partial source derived model | uniform_grid |
seed_reset | seed_reset | partial source derived model | seed_reset |
branch_relation | branch_relation | partial source derived model | branch_relation |
resource_cost | resource_cost | partial source derived model | resource_cost |
Model text
descriptant
mlab-rng-stream
Seed expansion applies four wrapping splitmix rounds; next_u64 returns rotl(s1*5,7)*9 then XOR/shift/rotl45 transition. Uniform=(result>>11)/2^53.
Epoch 2026-10-31: isolated source-bound fragment over bytes [386,1433); includes no claim beyond this relation. Source hash dccb613f518f32218a910c4eca3ad31df44347dd38b90d431833558e995a2046.
approximant
stream: forward relation
Seed expansion applies four wrapping splitmix rounds; next_u64 returns rotl(s1*5,7)*9 then XOR/shift/rotl45 transition. Uniform=(result>>11)/2^53.
Domain: All u64 seeds; IEEE f64 libm operations. Cross-platform transcendental bit identity is not proved.
Executable surrogate gap: no measured cheaper implementation with a useful scoped metric is supplied. Categorical/error/effect relations are exact obligations, not percent losses. Future numeric caps only1/2/5/10%.
invariant
stream: invariant and cost
Representable uniforms lie on j/2^53, 0<=j<2^53.
reseed replaces both state and spare; uniform draws do not consume spare.
Scope-specific cost: O(1) wrapping integer operations, four words; uniform consumes exactly one next_u64.
models
behavior_complement
Uniform excludes 1 and negative values; wrapping state arithmetic excludes debug overflow panics in the multiplications/addition explicitly marked wrapping.
reverse_reconstruction
A uniform value admits all low11-bit result antecedents plus compatible state words. Output alone does not recover the seed.
uniform_grid
Representable uniforms lie on j/2^53, 0<=j<2^53.
seed_reset
reseed replaces both state and spare; uniform draws do not consume spare.
branch_relation
Seed expansion applies four wrapping splitmix rounds; next_u64 returns rotl(s1*5,7)*9 then XOR/shift/rotl45 transition. Uniform=(result>>11)/2^53.
resource_cost
O(1) wrapping integer operations, four words; uniform consumes exactly one next_u64.
tests
Evidence boundary
See ../tests.md for the actual selected source test and mutant. These tests sample the file, not every fragment branch. Uniform excludes 1 and negative values; wrapping state arithmetic excludes debug overflow panics in the multiplications/addition explicitly marked wrapping. Other branches here are source-derived and unexecuted unless the parent test explicitly calls them.
This page in Markdown → https://md.groupants.elamur.ai/free/en/mova/mlab/src/rng.rs.groupant/stream.groupant/