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packages/foundation/random/pseudo-random/README.md
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# @suaveplan/pseudo-random - Deterministic seeded PRNG implementations (Mulberry32, SFC32, Xoshiro256++, CounterRng) with offset/fork/checkpoint/restore semantics
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## Summary
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Deterministic, seeded pseudo-random number generators (PRNGs) conforming to the `Rng` interface from `@suaveplan/types`. Ships four algorithms — Mulberry32, SFC32, Xoshiro256++, and CounterRng — with a unified `SeededRng` surface that includes `nextUint32`, `nextFloat`, `skip`, `at`, `fork`, `checkpoint`, and `restore`. Use this package when you need reproducible randomness (procedural generation, game simulations, property tests) or seek O(1) access to arbitrary positions in the sequence. For cryptographically secure randomness use `@suaveplan/random` (CSPRNG-backed) or `@suaveplan/crypto` (raw bytes). Utility functions `shuffle`, `sample`, `choice`, and `weightedChoice` accept any `Rng` and work with both seeded and crypto-backed sources.
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<!-- begin:auto-docs -->
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## Documentation tree
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- [counter-rng](./src/algorithms/counter-rng.md) — `CounterRng` is a hash-based PRNG: its output at logical position `i` is `splitmix64(seed XOR i)`. Because the output d…
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- [mulberry32](./src/algorithms/mulberry32.md) — `Mulberry32Rng` implements the Mulberry32 PRNG — a compact 32-bit linear-congruential-plus-mix generator with a period…
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- [sfc32](./src/algorithms/sfc32.md) — `Sfc32Rng` is a 128-bit SFC32 (Small Fast Counting) generator by Chris Doty-Humphrey. It carries four uint32 state word…
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- [xoshiro256](./src/algorithms/xoshiro256.md) — `Xoshiro256PlusPlusRng` implements Blackman and Vigna's Xoshiro256++ PRNG — 256 bits of state, period 2^256 − 1, with a…
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- [errors](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
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- [pseudo-random-error](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
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- [seed](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
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- [normalize](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_ <!-- end:auto-docs -->
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- [sample](./src/utils/sample.md) — The `sample` module covers the two sampling primitives that sit above `shuffle`: unique-without-replacement `sample` fo…
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- [shuffle](./src/utils/shuffle.md) — The `shuffle` module provides deterministic Fisher-Yates shuffling and single-element `choice` drawn from a user-suppli…
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<!-- end:auto-docs --> - [pseudo-random-error](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_- [seed](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [normalize](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [sample](./src/utils/sample.md) — The `sample` module covers the two sampling primitives that sit above `shuffle`: unique-without-replacement `sample` fo…
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- [shuffle](./src/utils/shuffle.md) — The `shuffle` module provides deterministic Fisher-Yates shuffling and single-element `choice` drawn from a user-suppli…
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- [pseudo-random-error](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_- [seed](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [normalize](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [sample](./src/utils/sample.md) — The `sample` module covers the two sampling primitives that sit above `shuffle`: unique-without-replacement `sample` fo…
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- [shuffle](./src/utils/shuffle.md) — The `shuffle` module provides deterministic Fisher-Yates shuffling and single-element `choice` drawn from a user-suppli…
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- [pseudo-random-error](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_- [seed](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [normalize](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [sample](./src/utils/sample.md) — The `sample` module covers the two sampling primitives that sit above `shuffle`: unique-without-replacement `sample` fo…
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- [shuffle](./src/utils/shuffle.md) — The `shuffle` module provides deterministic Fisher-Yates shuffling and single-element `choice` drawn from a user-suppli…
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- [pseudo-random-error](./src/errors/pseudo-random-error.md) — <!-- begin:auto-docs --> _(no submodules)_- [seed](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_ - [normalize](./src/seed/normalize.md) — <!-- begin:auto-docs --> _(no submodules)_- [sample](./src/utils/sample.md) — The `sample` module covers the two sampling primitives that sit above `shuffle`: unique-without-replacement `sample` fo…
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- [shuffle](./src/utils/shuffle.md) — The `shuffle` module provides deterministic Fisher-Yates shuffling and single-element `choice` drawn from a user-suppli…
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## Packages
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Four algorithms with identical `SeededRng` surface:
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| Algorithm | State | Period | Best for |
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| ------------------------- | ------ | ------------- | ------------------------------ |
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| `Mulberry32Rng` | 32 bit | ~2^32 | Tiny, per-UI seeding |
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| `Sfc32Rng` | 128bit | ≥2^32 | High-quality default |
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| `Xoshiro256PlusPlusRng` | 256bit | 2^256 − 1 | Simulations + parallel streams |
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| `CounterRng` | 64 bit | — | O(1) seek, procedural tiles |
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Each implements `nextUint32`, `nextFloat`, `skip`, `at`, `fork`, `checkpoint`, `restore`, plus `Xoshiro256PlusPlusRng.jump()` for jumping by 2^128 steps.
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## Install
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```sh
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bun add @suaveplan/pseudo-random
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```
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## Quick start
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```ts
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import { Sfc32Rng, shuffle } from "@suaveplan/pseudo-random";
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const rng = new Sfc32Rng("game-42");
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const deck = shuffle(["A", "K", "Q", "J"], rng);
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```
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## Subpath exports
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- `@suaveplan/pseudo-random/algorithms` — the four generators
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- `@suaveplan/pseudo-random/seed` — `normalizeSeed`, `splitmix32/64`, `expandSeed`
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- `@suaveplan/pseudo-random/utils` — `shuffle`, `sample`, `choice`, `weightedChoice`
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- `@suaveplan/pseudo-random/errors` — `PseudoRandomError`, `PSEUDO_RANDOM_CODES`
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- `@suaveplan/pseudo-random/schemas` — Zod schemas for serialised state
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## Module docs
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- [algorithms/mulberry32](./src/algorithms/mulberry32.md)
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- [algorithms/sfc32](./src/algorithms/sfc32.md)
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- [algorithms/xoshiro256](./src/algorithms/xoshiro256.md)
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- [algorithms/counter-rng](./src/algorithms/counter-rng.md)
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- [seed/normalize](./src/seed/normalize.md)
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- [utils/shuffle](./src/utils/shuffle.md)
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- [utils/sample](./src/utils/sample.md)
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- [errors](./src/errors/pseudo-random-error.md)
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- [types](./src/types/seeded-rng.types.md)
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