Struct CycleWalk 

pub struct CycleWalk {
    pub range: u64,
    pub seed: u64,
    pub stream: u64,
    pub state: CycleWalkState,
    /* private fields */
}

Bijective permutation of [0, range) via cycle-walking over PCG.

Signature: cycle_walk(position: u64, range: u64, seed: u64, stream: u64) -> u64

Maps every integer in [0, range) to a unique integer in [0, range) (a permutation). Internally uses a 6-round Feistel network operating on the bit-width of range, with PCG-derived round keys, then cycle-walks: if the Feistel output is >= range, it is fed back as input. Because the Feistel cipher is a bijection on the power-of-two domain and the mask is at most 2x range, each cycle-walk iteration has >= 50% chance of landing in range, giving fast expected termination (~2 iterations).

Use this when you need a shuffle or bijective mapping: e.g., visiting every row in a table exactly once in a pseudo-random order, or generating unique IDs without a tracking structure.

The range, seed, and stream are init-time constants.

JIT level: P3 (named JitOp consuming [range, seed, inc] from the jit_constants override); the compiled_u64 override serves the closure tier. Both read the pre-computed CycleWalkState.

Fields

range: u64

The range argument, as given at construction.

seed: u64

The seed argument, as given at construction.

stream: u64

The stream argument, as given at construction.

state: CycleWalkState

The state value, computed once at construction.

Implementations

impl CycleWalk

pub fn new(range: u64, seed: u64, stream: u64) -> Self

A cycle_walk node with the given constant arguments.

Trait Implementations

impl PolydatNode for CycleWalk

fn meta(&self) -> &NodeMeta

Return this node’s metadata (port names and types).

fn eval(&self, inputs: &[Value], outputs: &mut [Value])

Evaluate the node: read from inputs, write to outputs.

fn compiled_u64(&self) -> Option<CompiledU64Op>

Return a compiled u64-only evaluation closure, if this node operates entirely in u64 space.

fn compiled_slot(&self, wire_types: &[PortType]) -> Option<CompiledSlotKit>

Return a slot-compiled closure for nodes with typed-slice ports (§8.4 layer 3): slice inputs read (ptr, len) slot pairs; vector outputs write into kernel-owned scratch. Checked by the compiled-kernel builders AFTER Self::compiled_u64 — pure-scalar nodes never need it. Default None: the node stays on typed eval.

fn jit_constants(&self) -> Vec<u64>

Return assembly-time constants for JIT compilation.

fn scratch_layout(&self) -> Vec<ScratchElem>

The scratch entries a state owns for this node’s evaluation (axiom S3), one per entry in the order the node expects them in Self::eval_in. Empty for a node that evaluates over Values alone, which is every node but a native cone.

fn eval_in( &self, scratch: &mut [ScratchBuf], inputs: &[Value], outputs: &mut [Value], )

Self::eval with the node’s scratch, which the evaluating state owns and hands in: storage belongs to the state, never to the node, which is shared by every state of the program.

fn commutativity(&self) -> Commutativity

Declare which inputs are interchangeable for this node.

fn accepts_none_inputs(&self) -> bool

True iff this node should receive Value::None inputs directly rather than have the kernel propagate None through it. Default: false — most nodes follow SRD-74 Rule 1 (None in → None out, no eval invocation).

fn purity(&self) -> Purity

Declare this node’s purity status per the runtime_model.md’s D2 axiom. Default: Purity::Pure. Override to declare an observable side channel (Purity::SideChannel) or eval-call-spanning state (Purity::Nondeterministic).

fn simd_variant(&self) -> Option<SimdVariant>

Explicit SIMD-native implementation of this scalar node, if one has been registered with a semantic contract.

fn fusion_subgraph(&self) -> Option<FusionSubgraph<'_>>

A synthetic fusion node’s view of the subgraph it stands in for (SRD-105 cone extraction). Program-identity hashing (PolydatProgram::canonical_hash) walks THROUGH fusion nodes into this subgraph, so identity is invariant to the engine mix: jit=off and jit=auto compiles of the same source hash identically, and resume-skip matching survives mode changes. Default None: ordinary nodes hash as themselves.